@phdthesis{Lilienkamp2024,
  author    = {Lilienkamp, Henning},
  title     = {Enhanced computational approaches for data-driven characterization of earthquake ground motion and rapid earthquake impact assessment},
  doi       = {10.25932/publishup-63195},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-631954},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 145},
  year      = {2024},
  abstract  = {Rapidly growing seismic and macroseismic databases and simplified access to advanced machine learning methods have in recent years opened up vast opportunities to address challenges in engineering and strong motion seismology from novel, datacentric perspectives. In this thesis, I explore the opportunities of such perspectives for the tasks of ground motion modeling and rapid earthquake impact assessment, tasks with major implications for long-term earthquake disaster mitigation. In my first study, I utilize the rich strong motion database from the Kanto basin, Japan, and apply the U-Net artificial neural network architecture to develop a deep learning based ground motion model. The operational prototype provides statistical estimates of expected ground shaking, given descriptions of a specific earthquake source, wave propagation paths, and geophysical site conditions. The U-Net interprets ground motion data in its spatial context, potentially taking into account, for example, the geological properties in the vicinity of observation sites. Predictions of ground motion intensity are thereby calibrated to individual observation sites and earthquake locations. The second study addresses the explicit incorporation of rupture forward directivity into ground motion modeling. Incorporation of this phenomenon, causing strong, pulse like ground shaking in the vicinity of earthquake sources, is usually associated with an intolerable increase in computational demand during probabilistic seismic hazard analysis (PSHA) calculations. I suggest an approach in which I utilize an artificial neural network to efficiently approximate the average, directivity-related adjustment to ground motion predictions for earthquake ruptures from the 2022 New Zealand National Seismic Hazard Model. The practical implementation in an actual PSHA calculation demonstrates the efficiency and operational readiness of my model. In a follow-up study, I present a proof of concept for an alternative strategy in which I target the generalizing applicability to ruptures other than those from the New Zealand National Seismic Hazard Model. In the third study, I address the usability of pseudo-intensity reports obtained from macroseismic observations by non-expert citizens for rapid impact assessment. I demonstrate that the statistical properties of pseudo-intensity collections describing the intensity of shaking are correlated with the societal impact of earthquakes. In a second step, I develop a probabilistic model that, within minutes of an event, quantifies the probability of an earthquake to cause considerable societal impact. Under certain conditions, such a quick and preliminary method might be useful to support decision makers in their efforts to organize auxiliary measures for earthquake disaster response while results from more elaborate impact assessment frameworks are not yet available. The application of machine learning methods to datasets that only partially reveal characteristics of Big Data, qualify the majority of results obtained in this thesis as explorative insights rather than ready-to-use solutions to real world problems. The practical usefulness of this work will be better assessed in the future by applying the approaches developed to growing and increasingly complex data sets.},
  language  = {en}
}
@phdthesis{JimenezAlvaro2023,
  author    = {Jim{\´e}nez {\´A}lvaro, Eliana},
  title     = {An{\´a}lisis neotect{\´o}nico y lito-tefroestratigr{\´a}fico de los grandes movimientos en masa asociados al fallamiento activo de la cuenca intermontana Quito-Guayllabamba, Ecuador},
  doi       = {10.25932/publishup-62220},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-622209},
  school      = {Universit{\"a}t Potsdam},
  pages     = {195},
  year      = {2023},
  abstract  = {Within the Quito-Guayllabamba intermontane basin of Ecuador, five unusually large colluvial deposits of ancient landslides have been identified and analyzed in this study. The voluminous rotational MM-5 Guayllabamba landslide is the largest one, with a volume of 1183 million m3. The mega debris-avalanches MM-1 Conocoto, MM-3 Oyacoto, and MM-4 San Francisco were originally triggered by an initial rupture that was associated with a rotational landslide, the corresponding deposits have volumes between 399 to 317 million m3. Finally, the deposit with the smallest volume, the MM-2 Bat{\´a}n rotational landslide and debris fall, has a volume of 8,7 million m3. In this thesis, a detailed study of these large mass movements was carried out using neotectonic and litho-tephrostratigraphic methods to understand the geological and geomorphological boundary conditions that might have been relevant for triggering such mass movements. The neotectonic part of the study was based on the qualitative and quantitative geomorphic analysis of these large mass-movement deposits through the structural characterization of anticlines located east of the Quito sub-basin and their collapsed flanks that constitute the break-off areas. This part of the analysis was furthermore supported by the application of different morphometric indices to reveal tectonically forced landscape evolution processes that may have aided mass-movement generation. The litho-tephrostratigraphic part of the study was based on the analysis of petrographic, geochemical, and geochronological characteristics of soil horizons and intercalated volcanic ashes with the aim to constrain the timing of individual mass-movement events and their potential correlation. The results were integrated into chronostratigraphic schemes using break-off surfaces, cross-cutting and superposition relationships of landslide deposits and subsequently deposited strata to understand the mass movements in the tectonic and temporal context of the intermontane basin setting, as well as to identify the triggering mechanisms for each event. The MM-5 Guayllabamba mass movement is the result of the collapse of the southwestern slope of the Mojanda volcano and was triggered by the interaction of geologic and morphologic conditions approximately 0,81 Ma. The first debris-avalanche episode of the MM-3 Oyacoto and MM-4 San Francisco mass movements could be related to both geological and morphological conditions, given the highly fractured rocks and uplift of the Bellavista-Catequilla anticline that was subsequently incised at the foot of the slope by fluvial erosion. This first episode of collapse most likely occurred around 0,8 Ma. The MM-2 Bat{\´a}n mass movement was possibly also facilitated by a combination of geological and morphological conditions, most likely associated with a reduction in the lithostatic stresses affecting the Chiche and Mach{\´a}ngara formations and an increase of shear stresses during lateral fluvial scouring processes at the flanks of the source areas. This points to a linked process between river erosion and uplift processes associated with the evolution of the El Bat{\´a}n-La Bota anticline that could have occurred between 0,5 and 0,25 Ma. The voluminous MM-1 Conocoto debris avalanche, as well as the second debris avalanche episode that generated the MM-3 Oyacoto and MM-4 San Francisco mass movements, were caused by the gravitational collapse of the Mojanda and Cangahua formations that are characterized by the intercalation of volcanic ashes. The failure of the eastern flank of the anticlines probably was associated with increased available humidity related to regional Holocene climatic variations. The results of paleosol chronology combined with regional chronostratigraphic and paleoclimate data suggests that these debris avalanches were triggered between 5 and 4 ka. Active tectonics has shaped the morphological features of the Quito-Guayllabamba intermontane basin. The triggering of mass movements in this environment is associated with failure of Pleistocene lithologies (lake sediments, alluvial and volcanic deposits) subjected to ongoing deformation processes, seismic activity, and superposed episodes of climate variability. The Metropolitan District of Quito is an integral part of this complex environment and the geological, climatic, and topographic conditions that continue to influence the urban geographic space within this intermontane basin. The city of Quito comprises the area with the largest urban consolidation including the sub-basins of Quito and San Antonio, with a population of 2,872 million inhabitants, reflecting the importance of studying the inherent geological and climatic hazards that this region is confronted with.},
  language  = {es}
}
@phdthesis{Antonoglou2024,
  author    = {Antonoglou, Nikolaos},
  title     = {GNSS-based remote sensing: Innovative observation of key hydrological parameters in the Central Andes},
  doi       = {10.25932/publishup-62825},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-628256},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxii, 116},
  year      = {2024},
  abstract  = {The Central Andean region is characterized by diverse climate zones with sharp transitions between them. In this work, the area of interest is the South-Central Andes in northwestern Argentina that borders with Bolivia and Chile. The focus is the observation of soil moisture and water vapour with Global Navigation Satellite System (GNSS) remote-sensing methodologies. Because of the rapid temporal and spatial variations of water vapour and moisture circulations, monitoring this part of the hydrological cycle is crucial for understanding the mechanisms that control the local climate. Moreover, GNSS-based techniques have previously shown high potential and are appropriate for further investigation. This study includes both logistic-organization effort and data analysis. As for the prior, three GNSS ground stations were installed in remote locations in northwestern Argentina to acquire observations, where there was no availability of third-party data. The methodological development for the observation of the climate variables of soil moisture and water vapour is independent and relies on different approaches. The soil-moisture estimation with GNSS reflectometry is an approximation that has demonstrated promising results, but it has yet to be operationally employed. Thus, a more advanced algorithm that exploits more observations from multiple satellite constellations was developed using data from two pilot stations in Germany. Additionally, this algorithm was slightly modified and used in a sea-level measurement campaign. Although the objective of this application is not related to monitoring hydrological parameters, its methodology is based on the same principles and helps to evaluate the core algorithm. On the other hand, water-vapour monitoring with GNSS observations is a well-established technique that is utilized operationally. Hence, the scope of this study is conducting a meteorological analysis by examining the along-the-zenith air-moisture levels and introducing indices related to the azimuthal gradient. The results of the experiments indicate higher-quality soil moisture observations with the new algorithm. Furthermore, the analysis using the stations in northwestern Argentina illustrates the limits of this technology because of varying soil conditions and shows future research directions. The water-vapour analysis points out the strong influence of the topography on atmospheric moisture circulation and rainfall generation. Moreover, the GNSS time series allows for the identification of seasonal signatures, and the azimuthal-gradient indices permit the detection of main circulation pathways.},
  language  = {en}
}
@phdthesis{Manu2023,
  author    = {Manu, Evans},
  title     = {Hydrogeochemical characterization of water resources in the Pra Basin (Ghana) for quality assessment and water management},
  doi       = {10.25932/publishup-62806},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-628062},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 106},
  year      = {2023},
  abstract  = {Watershed management requires an understanding of key hydrochemical processes. The Pra Basin is one of the five major river basins in Ghana with a population of over 4.2 million people. Currently, water resources management faces challenges due to surface water pollution caused by the unregulated release of untreated household and industrial waste into aquatic ecosystems and illegal mining activities. This has increased the need for groundwater as the most reliable water supply. Our understanding of groundwater recharge mechanisms and chemical evolution in the basin has been inadequate, making effective management difficult. Therefore, the main objective of this work is to gain insight into the processes that determine the hydrogeochemical evolution of groundwater quality in the Pra Basin. The combined use of stable isotope, hydrochemistry, and water level data provides the basis for conceptualizing the chemical evolution of groundwater in the Pra Basin. For this purpose, the origin and evaporation rates of water infiltrating into the unsaturated zone were evaluated. In addition, Chloride Mass Balance (CMB) and Water Table Fluctuations (WTF) were considered to quantify groundwater recharge for the basin. Indices such as water quality index (WQI), sodium adsorption ratio (SAR), Wilcox diagram, and salinity (USSL) were used in this study to determine the quality of the resource for use as drinking water and for irrigation purposes. Due to the heterogeneity of the hydrochemical data, the statistical techniques of hierarchical cluster and factor analysis were applied to subdivide the data according to their spatial correlation. A conceptual hydrogeochemical model was developed and subsequently validated by applying combinatorial inverse and reaction pathway-based geochemical models to determine plausible mineral assemblages that control the chemical composition of the groundwater. The interactions between water and rock determine the groundwater quality in the Pra Basin. The results underline that the groundwater is of good quality and can be used for drinking water and irrigation purposes. It was demonstrated that there is a large groundwater potential to meet the entire Pra Basin's current and future water demands. The main recharge area was identified as the northern zone, while the southern zone is the discharge area. The predominant influence of weathering of silicate minerals plays a key role in the chemical evolution of the groundwater. The work presented here provides fundamental insights into the hydrochemistry of the Pra Basin and provides data important to water managers for informed decision-making in planning and allocating water resources for various purposes. A novel inverse modelling approach was used in this study to identify different mineral compositions that determine the chemical evolution of groundwater in the Pra Basin. This modelling technique has the potential to simulate the composition of groundwater at the basin scale with large hydrochemical heterogeneity, using average water composition to represent established spatial groupings of water chemistry.},
  language  = {en}
}
@phdthesis{Mueller2024,
  author    = {M{\"u}ller, Daniel},
  title     = {Identification and monitoring of structures, controls, and evolution dynamics of hydrothermal systems and associated alteration through high-resolution remote sensing and in situ analysis},
  doi       = {10.25932/publishup-62668},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-626683},
  school      = {Universit{\"a}t Potsdam},
  pages     = {205},
  year      = {2024},
  abstract  = {Volcanic hydrothermal systems are an integral part of most volcanoes and typically involve a heat source, adequate fluid supply, and fracture or pore systems through which the fluids can circulate within the volcanic edifice. Associated with this are subtle but powerful processes that can significantly influence the evolution of volcanic activity or the stability of the near-surface volcanic system through mechanical weakening, permeability reduction, and sealing of the affected volcanic rock. These processes are well constrained for rock samples by laboratory analyses but are still difficult to extrapolate and evaluate at the scale of an entire volcano. Advances in unmanned aircraft systems (UAS), sensor technology, and photogrammetric processing routines now allow us to image volcanic surfaces at the centimeter scale and thus study volcanic hydrothermal systems in great detail. This thesis aims to explore the potential of UAS approaches for studying the structures, processes, and dynamics of volcanic hydrothermal systems but also to develop methodological approaches to uncover secondary information hidden in the data, capable of indicating spatiotemporal dynamics or potentially critical developments associated with hydrothermal alteration. To accomplish this, the thesis describes the investigation of two near-surface volcanic hydrothermal systems, the El Tatio geyser field in Chile and the fumarole field of La Fossa di Vulcano (Italy), both of which are among the best-studied sites of their kind. Through image analysis, statistical, and spatial analyses we have been able to provide the most detailed structural images of both study sites to date, with new insights into the driving forces of such systems but also revealing new potential controls, which are summarized in conceptual site-specific models. Furthermore, the thesis explores methodological remote sensing approaches to detect, classify and constrain hydrothermal alteration and surface degassing from UAS-derived data, evaluated them by mineralogical and chemical ground-truthing, and compares the alteration pattern with the present-day degassing activity. A significant contribution of the often neglected diffuse degassing activity to the total amount of degassing is revealed and constrains secondary processes and dynamics associated with hydrothermal alteration that lead to potentially critical developments like surface sealing. The results and methods used provide new approaches for alteration research, for the monitoring of degassing and alteration effects, and for thermal monitoring of fumarole fields, with the potential to be incorporated into volcano monitoring routines.},
  language  = {en}
}
@phdthesis{WindirschWoiwode2024,
  author    = {Windirsch-Woiwode, Torben},
  title     = {Permafrost carbon stabilisation by recreating a herbivore-driven ecosystem},
  doi       = {10.25932/publishup-62424},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-624240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 104, A-57},
  year      = {2024},
  abstract  = {With Arctic ground as a huge and temperature-sensitive carbon reservoir, maintaining low ground temperatures and frozen conditions to prevent further carbon emissions that contrib-ute to global climate warming is a key element in humankind's fight to maintain habitable con-ditions on earth. Former studies showed that during the late Pleistocene, Arctic ground condi-tions were generally colder and more stable as the result of an ecosystem dominated by large herbivorous mammals and vast extents of graminoid vegetation - the mammoth steppe. Characterised by high plant productivity (grassland) and low ground insulation due to animal-caused compression and removal of snow, this ecosystem enabled deep permafrost aggrad-ation. Now, with tundra and shrub vegetation common in the terrestrial Arctic, these effects are not in place anymore. However, it appears to be possible to recreate this ecosystem local-ly by artificially increasing animal numbers, and hence keep Arctic ground cold to reduce or-ganic matter decomposition and carbon release into the atmosphere. By measuring thaw depth, total organic carbon and total nitrogen content, stable carbon iso-tope ratio, radiocarbon age, n-alkane and alcohol characteristics and assessing dominant vegetation types along grazing intensity transects in two contrasting Arctic areas, it was found that recreating conditions locally, similar to the mammoth steppe, seems to be possible. For permafrost-affected soil, it was shown that intensive grazing in direct comparison to non-grazed areas reduces active layer depth and leads to higher TOC contents in the active layer soil. For soil only frozen on top in winter, an increase of TOC with grazing intensity could not be found, most likely because of confounding factors such as vertical water and carbon movement, which is not possible with an impermeable layer in permafrost. In both areas, high animal activity led to a vegetation transformation towards species-poor graminoid-dominated landscapes with less shrubs. Lipid biomarker analysis revealed that, even though the available organic material is different between the study areas, in both permafrost-affected and sea-sonally frozen soils the organic material in sites affected by high animal activity was less de-composed than under less intensive grazing pressure. In conclusion, high animal activity af-fects decomposition processes in Arctic soils and the ground thermal regime, visible from reduced active layer depth in permafrost areas. Therefore, grazing management might be utilised to locally stabilise permafrost and reduce Arctic carbon emissions in the future, but is likely not scalable to the entire permafrost region.},
  language  = {en}
}
@phdthesis{Schifferle2024,
  author    = {Schifferle, Lukas},
  title     = {Optical properties of (Mg,Fe)O at high pressure},
  doi       = {10.25932/publishup-62216},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-622166},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIV, 90},
  year      = {2024},
  abstract  = {Large parts of the Earth's interior are inaccessible to direct observation, yet global geodynamic processes are governed by the physical material properties under extreme pressure and temperature conditions. It is therefore essential to investigate the deep Earth's physical properties through in-situ laboratory experiments. With this goal in mind, the optical properties of mantle minerals at high pressure offer a unique way to determine a variety of physical properties, in a straight-forward, reproducible, and time-effective manner, thus providing valuable insights into the physical processes of the deep Earth. This thesis focusses on the system Mg-Fe-O, specifically on the optical properties of periclase (MgO) and its iron-bearing variant ferropericlase ((Mg,Fe)O), forming a major planetary building block. The primary objective is to establish links between physical material properties and optical properties. In particular the spin transition in ferropericlase, the second-most abundant phase of the lower mantle, is known to change the physical material properties. Although the spin transition region likely extends down to the core-mantle boundary, the ef-fects of the mixed-spin state, where both high- and low-spin state are present, remains poorly constrained. In the studies presented herein, we show how optical properties are linked to physical properties such as electrical conductivity, radiative thermal conductivity and viscosity. We also show how the optical properties reveal changes in the chemical bonding. Furthermore, we unveil how the chemical bonding, the optical and other physical properties are affected by the iron spin transition. We find opposing trends in the pres-sure dependence of the refractive index of MgO and (Mg,Fe)O. From 1 atm to ~140 GPa, the refractive index of MgO decreases by ~2.4\% from 1.737 to 1.696 (±0.017). In contrast, the refractive index of (Mg0.87Fe0.13)O (Fp13) and (Mg0.76Fe0.24)O (Fp24) ferropericlase increases with pressure, likely because Fe Fe interactions between adjacent iron sites hinder a strong decrease of polarizability, as it is observed with increasing density in the case of pure MgO. An analysis of the index dispersion in MgO (decreasing by ~23\% from 1 atm to ~103 GPa) reflects a widening of the band gap from ~7.4 eV at 1 atm to ~8.5 (±0.6) eV at ~103 GPa. The index dispersion (between 550 and 870 nm) of Fp13 reveals a decrease by a factor of ~3 over the spin transition range (~44-100 GPa). We show that the electrical band gap of ferropericlase significantly widens up to ~4.7 eV in the mixed spin region, equivalent to an increase by a factor of ~1.7. We propose that this is due to a lower electron mobility between adjacent Fe2+ sites of opposite spin, explaining the previously observed low electrical conductivity in the mixed spin region. From the study of absorbance spectra in Fp13, we show an increasing covalency of the Fe-O bond with pressure for high-spin ferropericlase, whereas in the low-spin state a trend to a more ionic nature of the Fe-O bond is observed, indicating a bond weakening effect of the spin transition. We found that the spin transition is ultimately caused by both an increase of the ligand field-splitting energy and a decreasing spin-pairing energy of high-spin Fe2+.},
  language  = {en}
}
@phdthesis{LauerDuenkelberg2023,
  author    = {Lauer-D{\"u}nkelberg, Gregor},
  title     = {Extensional deformation and landscape evolution of the Central Andean Plateau},
  doi       = {10.25932/publishup-61759},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617593},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xviii, 195},
  year      = {2023},
  abstract  = {Mountain ranges can fundamentally influence the physical and and chemical processes that shape Earths' surface. With elevations of up to several kilometers they create climatic enclaves by interacting with atmospheric circulation and hydrologic systems, thus leading to a specific distribution of flora and fauna. As a result, the interiors of many Cenozoic mountain ranges are characterized by an arid climate, internally drained and sediment-filled basins, as well as unique ecosystems that are isolated from the adjacent humid, low-elevation regions along their flanks and forelands. These high-altitude interiors of orogens are often characterized by low relief and coalesced sedimentary basins, commonly referred to as plateaus, tectono-geomorphic entities that result from the complex interactions between mantle-driven geological and tectonic conditions and superposed atmospheric and hydrological processes. The efficiency of these processes and the fate of orogenic plateaus is therefore closely tied to the balance of constructive and destructive processes - tectonic uplift and erosion, respectively. In numerous geological studies it has been shown that mountain ranges are delicate systems that can be obliterated by an imbalance of these underlying forces. As such, Cenozoic mountain ranges might not persist on long geological timescales and will be destroyed by erosion or tectonic collapse. Advancing headward erosion of river systems that drain the flanks of the orogen may ultimately sever the internal drainage conditions and the maintenance of storage of sediments within the plateau, leading to destruction of plateau morphology and connectivity with the foreland. Orogenic collapse may be associated with the changeover from a compressional stress field with regional shortening and topographic growth, to a tensional stress field with regional extensional deformation and ensuing incision of the plateau. While the latter case is well-expressed by active extensional faults in the interior parts of the Tibetan Plateau and the Himalaya, for example, the former has been attributed to have breached the internally drained areas of the high-elevation sectors of the Iranian Plateau. In the case of the Andes of South America and their internally drained Altiplano-Puna Plateau, signs of both processes have been previously described. However, in the orogenic collapse scenario the nature of the extensional structures had been primarily investigated in the northern and southern terminations of the plateau; in some cases, the extensional faults were even regarded to be inactive. After a shallow earthquake in 2020 within the Eastern Cordillera of Argentina that was associated with extensional deformation, the state of active deformation and the character of the stress field in the central parts of the plateau received renewed interest to explain a series of extensional structures in the northernmost sectors of the plateau in north-western Argentina. This study addresses (1) the issue of tectonic orogenic collapse of the Andes and the destruction of plateau morphology by studying the fill and erosion history of the central eastern Andean Plateau using sedimentological and geochronological data and (2) the kinematics, timing and magnitude of extensional structures that form well-expressed fault scarps in sediments of the regional San Juan del Oro surface, which is an integral part of the Andean Plateau and adjacent morphotectonic provinces to the east. Importantly, sediment properties and depositional ages document that the San Juan del Oro Surface was not part of the internally-drained Andean Plateau, but rather associated with a foreland-directed drainage system, which was modified by the Andean orogeny and that became successively incorporated into the orogen by the eastward-migration of the Andean deformation front during late Miocene - Pliocene time. Structural and geomorphic observations within the plateau indicate that extensional processes must have been repeatedly active between the late Miocene and Holocene supporting the notion of plateau-wide extensional processes, potentially associated with Mw ~ 7 earthquakes. The close relationship between extensional joints and fault orientations underscores that 3 was oriented horizontally in NW-SE direction and 1 was vertical. This unambiguously documents that the observed deformation is related to gravitational forces that drive the orogenic collapse of the plateau. Applied geochronological analyses suggest that normal faulting in the northern Puna was active at about 3 Ma, based on paired cosmogenic nuclide dating of sediment fill units. Possibly due to regional normal faulting the drainage system within the plateau was modified, promoting fluvial incision.},
  language  = {en}
}
@phdthesis{QuirogaCarrasco2023,
  author    = {Quiroga Carrasco, Rodrigo Adolfo},
  title     = {Cenozoic style of deformation and spatiotemporal variations of the tectonic stress field in the southern central Andes},
  doi       = {10.25932/publishup-61038},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610387},
  school      = {Universit{\"a}t Potsdam},
  pages     = {228},
  year      = {2023},
  abstract  = {The central Andean plateau is the second largest orogenic plateau in the world and has formed in a non-collisional orogenic system. It extends from southern Peru (15°S) to northern Argentina and Chile (27°30'S) and reaches an average elevation of 4,000 m.a.s.l. South of 24°S, the Andean plateau is called Puna and it is characterized by a system of endorheic basins with thick sequences where clastic and evaporitic strata are preserved. Between 26° and 27°30'S, the Puna terminates in a structurally complex zone which coincides with the transition from a normal subduction zone to a flat subduction ("flat slab") zone, which extends to 33°S. This transition zone also coincides with important morphostructural provinces that, from west to east, correspond to i) the Cordillera Frontal, where the Maricunga Belt is located; ii) the Famatina system; and iv) the north-western, thick-skinned Sierras Pampeanas. Various structural, sedimentological, thermochronological and geochronological studies in this region have documented a complex history of deformation and uplift during successive Cenozoic deformation events. These processes caused the increase of crustal thickness, as well as episodes of diachronic uplift, which attained its present configuration during the late Miocene. Subsequently, the plateau experienced a change in deformation style from contraction to extension and transtension documented by ubiquitous normal faults, earthquakes, and magmatic rocks. However, at the southern edge of the Puna plateau and in the transition to the other morphostructural provinces, the variation of deformation processes and the changes in the tectonic stress field are not fully understood. This location is thus ideally located to evaluate how the tectonic stress field may have evolved and how it may have been affected by the presence/absence of an orogenic plateau, as well as by the existence of inherited structural anisotropies within the different tectonic provinces. This thesis investigates the relationship between shallow crustal deformation and the spatiotemporal evolution of the tectonic stress field in the southern sector of the Andean plateau, during pre-, syn- and post-uplift periods of this plateau. To carry out this research, multiple methodological approaches were chosen that include (U-Pb) radiometric dating; the analysis of mesoscopic faults to obtain stress tensors and the orientation of the principal stress axes; the determination of magnetic susceptibility anisotropy in sedimentary and volcanoclastic rocks to identify shortening directions or directions of sedimentary transport; kinematic modeling to infer deep crustal structures and deformation; and finally, a morphometric analysis to identify geomorphological indicators associated with Quaternary tectonism. Combining the obtained results with data from published studies, this study reveals a complex history of the tectonic stress field that has been characterized by changes in orientation and by vertical permutations of the principal stress axes during each deformation regime over the last ~24 Ma. The evolution of the tectonic stress field can be linked with three orogenic phases at this latitude of the Andean orogen: (1) a first phase with an E-W-oriented compression documented between Eocene and middle Miocene, which coincided with Andean crustal thickening, lateral growth, and topographic uplift; (2) a second phase characterized by a compressive transpressional stress regime, starting at ~11 Ma and ~5 Ma on the western and eastern edge of the Puna plateau, respectively, and a compressive stress regime in the Famatina system and the Sierras Pampeanas, which is interpreted to reflect a transition between Neogene orogenic construction and the maximum accumulation of deformation and topographic uplift of the Puna plateau; and (3) a third phase, when the tectonic regime caused a changeover to a tensional stress state that followed crustal thickening and the maximum uplift of the plateau between ~5-4 Ma; this is especially well expressed in the Puna, in its western border area with the Maricunga-Valle Ancho Belt, and along its eastern border in the transition with the Sierras Pampeanas. The results of the study thus document that the plateau rim experienced a shift from a compressional to a transtensional regime, which differs from the tensional state of stress of the Andean Plateau in the northern sectors for the same period. Similar stress changes have been documented during the construction of the Tibetan plateau, where a predominantly compressional stress regime changed to a transtensional regime, but which was superseded by a purely tensional regime, between 14 and 4 Ma.},
  language  = {es}
}
@phdthesis{Metz2023,
  author    = {Metz, Malte},
  title     = {Finite fault earthquake source inversions},
  doi       = {10.25932/publishup-61974},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-619745},
  school      = {Universit{\"a}t Potsdam},
  pages     = {143},
  year      = {2023},
  abstract  = {Earthquake modeling is the key to a profound understanding of a rupture. Its kinematics or dynamics are derived from advanced rupture models that allow, for example, to reconstruct the direction and velocity of the rupture front or the evolving slip distribution behind the rupture front. Such models are often parameterized by a lattice of interacting sub-faults with many degrees of freedom, where, for example, the time history of the slip and rake on each sub-fault are inverted. To avoid overfitting or other numerical instabilities during a finite-fault estimation, most models are stabilized by geometric rather than physical constraints such as smoothing. As a basis for the inversion approach of this study, we build on a new pseudo-dynamic rupture model (PDR) with only a few free parameters and a simple geometry as a physics-based solution of an earthquake rupture. The PDR derives the instantaneous slip from a given stress drop on the fault plane, with boundary conditions on the developing crack surface guaranteed at all times via a boundary element approach. As a side product, the source time function on each point on the rupture plane is not constraint and develops by itself without additional parametrization. The code was made publicly available as part of the Pyrocko and Grond Python packages. The approach was compared with conventional modeling for different earthquakes. For example, for the Mw 7.1 2016 Kumamoto, Japan, earthquake, the effects of geometric changes in the rupture surface on the slip and slip rate distributions could be reproduced by simply projecting stress vectors. For the Mw 7.5 2018 Palu, Indonesia, strike-slip earthquake, we also modelled rupture propagation using the 2D Eikonal equation and assuming a linear relationship between rupture and shear wave velocity. This allowed us to give a deeper and faster propagating rupture front and the resulting upward refraction as a new possible explanation for the apparent supershear observed at the Earth's surface. The thesis investigates three aspects of earthquake inversion using PDR: (1) to test whether implementing a simplified rupture model with few parameters into a probabilistic Bayesian scheme without constraining geometric parameters is feasible, and whether this leads to fast and robust results that can be used for subsequent fast information systems (e.g., ground motion predictions). (2) To investigate whether combining broadband and strong-motion seismic records together with near-field ground deformation data improves the reliability of estimated rupture models in a Bayesian inversion. (3) To investigate whether a complex rupture can be represented by the inversion of multiple PDR sources and for what type of earthquakes this is recommended. I developed the PDR inversion approach and applied the joint data inversions to two seismic sequences in different tectonic settings. Using multiple frequency bands and a multiple source inversion approach, I captured the multi-modal behaviour of the Mw 8.2 2021 South Sandwich subduction earthquake with a large, curved and slow rupturing shallow earthquake bounded by two faster and deeper smaller events. I could cross-validate the results with other methods, i.e., P-wave energy back-projection, a clustering analysis of aftershocks and a simple tsunami forward model. The joint analysis of ground deformation and seismic data within a multiple source inversion also shed light on an earthquake triplet, which occurred in July 2022 in SE Iran. From the inversion and aftershock relocalization, I found indications for a vertical separation between the shallower mainshocks within the sedimentary cover and deeper aftershocks at the sediment-basement interface. The vertical offset could be caused by the ductile response of the evident salt layer to stress perturbations from the mainshocks. The applications highlight the versatility of the simple PDR in probabilistic seismic source inversion capturing features of rather different, complex earthquakes. Limitations, as the evident focus on the major slip patches of the rupture are discussed as well as differences to other finite fault modeling methods.},
  language  = {en}
}
@phdthesis{Kooten2023,
  author    = {Kooten, Willemijn Sarah Maria Theresia van},
  title     = {Structural inheritance of the Salta Rift basin and its control on exhumation patterns of the Eastern Cordillera between 23 and 24°S},
  doi       = {10.25932/publishup-61798},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617983},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIX, 188},
  year      = {2023},
  abstract  = {The deformation style of mountain belts is greatly influenced by the upper plate architecture created during preceding deformation phases. The Mesozoic Salta Rift extensional phase has created a dominant structural and lithological framework that controls Cenozoic deformation and exhumation patterns in the Central Andes. Studying the nature of these pre-existing anisotropies is a key to understanding the spatiotemporal distribution of exhumation and its controlling factors. The Eastern Cordillera in particular, has a structural grain that is in part controlled by Salta Rift structures and their orientation relative to Andean shortening. As a result, there are areas in which Andean deformation prevails and areas where the influence of the Salta Rift is the main control on deformation patterns. Between 23 and 24°S, lithological and structural heterogeneities imposed by the Lomas de Olmedo sub-basin (Salta Rift basin) affect the development of the Eastern Cordillera fold-and-thrust belt. The inverted northern margin of the sub-basin now forms the southern boundary of the intermontane Cianzo basin. The former western margin of the sub-basin is located at the confluence of the Subandean Zone, the Santa Barbara System and the Eastern Cordillera. Here, the Salta Rift basin architecture is responsible for the distribution of these morphotectonic provinces. In this study we use a multi-method approach consisting of low-temperature (U-Th-Sm)/He and apatite fission track thermochronology, detrital geochronology, structural and sedimentological analyses to investigate the Mesozoic structural inheritance of the Lomas de Olmedo sub-basin and Cenozoic exhumation patterns. Characterization of the extension-related Tacur{\´u} Group as an intermediate succession between Paleozoic basement and the syn-rift infill of the Lomas de Olmedo sub-basin reveals a Jurassic maximum depositional age. Zircon (U-Th-Sm)/He cooling ages record a pre-Cretaceous onset of exhumation for the rift shoulders in the northern part of the sub-basin, whereas the western shoulder shows a more recent onset (140-115 Ma). Variations in the sedimentary thickness of syn- and post-rift strata document the evolution of accommodation space in the sub-basin. While the thickness of syn-rift strata increases rapidly toward the northern basin margin, the post-rift strata thickness decreases toward the margin and forms a condensed section on the rift shoulder. Inversion of Salta Rift structures commenced between the late Oligocene and Miocene (24-15 Ma) in the ranges surrounding the Cianzo basin. The eastern and western limbs of the Cianzo syncline, located in the hanging wall of the basin-bounding Hornocal fault, show diachronous exhumation. At the same time, western fault blocks of Tilcara Range, south of the Cianzo basin, began exhuming in the late Oligocene to early Miocene (26-16 Ma). Eastward propagation to the frontal thrust and to the Paleozoic strata east of the Tilcara Range occurred in the middle Miocene (22-10 Ma) and the late Miocene-early Pliocene (10-4 Ma), respectively.},
  language  = {en}
}
@phdthesis{Mantiloni2023,
  author    = {Mantiloni, Lorenzo},
  title     = {Modeling stress and dike pathways in calerdas},
  doi       = {10.25932/publishup-61262},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-612621},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 145},
  year      = {2023},
  abstract  = {Volcanic hazard assessment relies on physics-based models of hazards, such as lava flows and pyroclastic density currents, whose outcomes are very sensitive to the location where future eruptions will occur. On the contrary, forecast of vent opening locations in volcanic areas typically relies on purely data-driven approaches, where the spatial density of past eruptive vents informs the probability maps of future vent opening. Such techniques may be suboptimal in volcanic systems with missing or scarce data, and where the controls on magma pathways may change over time. An alternative approach was recently proposed, relying on a model of stress-driven pathways of magmatic dikes. In that approach, the crustal stress was optimized so that dike trajectories linked consistently the location of the magma chamber to that of past vents. The retrieved information on the stress state was then used to forecast future dike trajectories. The validation of such an approach requires extensive application to nature. Before doing so, however, several important limitations need to be removed, most importantly the two-dimensional (2D) character of the models and theoretical concepts. In this thesis, I develop methods and tools so that a physics-based strategy of stress inversion and eruptive vent forecast in volcanoes can be applied to three dimensional (3D) problems. In the first part, I test the stress inversion and vent forecast strategy on analog models, still within a 2D framework, but improving on the efficiency of the stress optimization. In the second part, I discuss how to correctly account for gravitational loading/unloading due to complex 3D topography with a Boundary-Element numerical model. Then, I develop a new, simplified but fast model of dike pathways in 3D, designed for running large numbers of simulations at minimal computational cost, and able to backtrack dike trajectories from vents on the surface. Finally, I combine the stress and dike models to simulate dike pathways in synthetic calderas. In the third part, I describe a framework of stress inversion and vent forecast strategy in 3D for calderas. The stress inversion relies on, first, describing the magma storage below a caldera in terms of a probability density function. Next, dike trajectories are backtracked from the known locations of past vents down through the crust, and the optimization algorithm seeks for the stress models which lead trajectories through the regions of highest probability. I apply the new strategy to the synthetic scenarios presented in the second part, and I exploit the results from the stress inversions to produce probability maps of future vent locations for some of those scenarios. In the fourth part, I present the inversion of different deformation source models applied to the ongoing ground deformation observed across the Rhenish Massif in Central Europe. The region includes the Eifel Volcanic Fields in Germany, a potential application case for the vent forecast strategy. The results show how the observed deformation may be due to melt accumulation in sub-horizontal structures in the lower crust or upper mantle. The thesis concludes with a discussion of the stress inversion and vent forecast strategy, its limitations and applicability to real volcanoes. Potential developments of the modeling tools and concepts presented here are also discussed, as well as possible applications to other geophysical problems.},
  language  = {en}
}
@phdthesis{Stoltnow2023,
  author    = {Stoltnow, Malte},
  title     = {Magmatic-hydrothermal processes along the porphyry to epithermal transition},
  doi       = {10.25932/publishup-61140},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-611402},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxviii, 132},
  year      = {2023},
  abstract  = {Magmatic-hydrothermal systems form a variety of ore deposits at different proximities to upper-crustal hydrous magma chambers, ranging from greisenization in the roof zone of the intrusion, porphyry mineralization at intermediate depths to epithermal vein deposits near the surface. The physical transport processes and chemical precipitation mechanisms vary between deposit types and are often still debated. The majority of magmatic-hydrothermal ore deposits are located along the Pacific Ring of Fire, whose eastern part is characterized by the Mesozoic to Cenozoic orogenic belts of the western North and South Americas, namely the American Cordillera. Major magmatic-hydrothermal ore deposits along the American Cordillera include (i) porphyry Cu(-Mo-Au) deposits (along the western cordilleras of Mexico, the western U.S., Canada, Chile, Peru, and Argentina); (ii) Climax- (and sub-) type Mo deposits (Colorado Mineral Belt and northern New Mexico); and (iii) porphyry and IS-type epithermal Sn(-W-Ag) deposits of the Central Andean Tin Belt (Bolivia, Peru and northern Argentina). The individual studies presented in this thesis primarily focus on the formation of different styles of mineralization located at different proximities to the intrusion in magmatic-hydrothermal systems along the American Cordillera. This includes (i) two individual geochemical studies on the Sweet Home Mine in the Colorado Mineral Belt (potential endmember of peripheral Climax-type mineralization); (ii) one numerical modeling study setup in a generic porphyry Cu-environment; and (iii) a numerical modeling study on the Central Andean Tin Belt-type Pirquitas Mine in NW Argentina. Microthermometric data of fluid inclusions trapped in greisen quartz and fluorite from the Sweet Home Mine (Detroit City Portal) suggest that the early-stage mineralization precipitated from low- to medium-salinity (1.5-11.5 wt.\% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415°C and at depths of at least 3.5 km. Stable isotope and noble gas isotope data indicate that greisen formation and base metal mineralization at the Sweet Home Mine was related to fluids of different origins. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases), which subsequently mixed with significant amounts of heated meteoric water. Mixing of magmatic fluids with meteoric water is constrained by δ2Hw-δ18Ow relationships of fluid inclusions. The deep hydrothermal mineralization at the Sweet Home Mine shows features similar to deep hydrothermal vein mineralization at Climax-type Mo deposits or on their periphery. This suggests that fluid migration and the deposition of ore and gangue minerals in the Sweet Home Mine was triggered by a deep-seated magmatic intrusion. The second study on the Sweet Home Mine presents Re-Os molybdenite ages of 65.86±0.30 Ma from a Mo-mineralized major normal fault, namely the Contact Structure, and multimineral Rb-Sr isochron ages of 26.26±0.38 Ma and 25.3±3.0 Ma from gangue minerals in greisen assemblages. The age data imply that mineralization at the Sweet Home Mine formed in two separate events: Late Cretaceous (Laramide-related) and Oligocene (Rio Grande Rift-related). Thus, the age of Mo mineralization at the Sweet Home Mine clearly predates that of the Oligocene Climax-type deposits elsewhere in the Colorado Mineral Belt. The Re-Os and Rb-Sr ages also constrain the age of the latest deformation along the Contact Structure to between 62.77±0.50 Ma and 26.26±0.38 Ma, which was employed and/or crosscut by Late Cretaceous and Oligocene fluids. Along the Contact Structure Late Cretaceous molybdenite is spatially associated with Oligocene minerals in the same vein system, a feature that precludes molybdenite recrystallization or reprecipitation by Oligocene ore fluids. Ore precipitation in porphyry copper systems is generally characterized by metal zoning (Cu-Mo to Zn-Pb-Ag), which is suggested to be variably related to solubility decreases during fluid cooling, fluid-rock interactions, partitioning during fluid phase separation and mixing with external fluids. The numerical modeling study setup in a generic porphyry Cu-environment presents new advances of a numerical process model by considering published constraints on the temperature- and salinity-dependent solubility of Cu, Pb and Zn in the ore fluid. This study investigates the roles of vapor-brine separation, halite saturation, initial metal contents, fluid mixing, and remobilization as first-order controls of the physical hydrology on ore formation. The results show that the magmatic vapor and brine phases ascend with different residence times but as miscible fluid mixtures, with salinity increases generating metal-undersaturated bulk fluids. The release rates of magmatic fluids affect the location of the thermohaline fronts, leading to contrasting mechanisms for ore precipitation: higher rates result in halite saturation without significant metal zoning, lower rates produce zoned ore shells due to mixing with meteoric water. Varying metal contents can affect the order of the final metal precipitation sequence. Redissolution of precipitated metals results in zoned ore shell patterns in more peripheral locations and also decouples halite saturation from ore precipitation. The epithermal Pirquitas Sn-Ag-Pb-Zn mine in NW Argentina is hosted in a domain of metamorphosed sediments without geological evidence for volcanic activity within a distance of about 10 km from the deposit. However, recent geochemical studies of ore-stage fluid inclusions indicate a significant contribution of magmatic volatiles. This study tested different formation models by applying an existing numerical process model for porphyry-epithermal systems with a magmatic intrusion located either at a distance of about 10 km underneath the nearest active volcano or hidden underneath the deposit. The results show that the migration of the ore fluid over a 10-km distance results in metal precipitation by cooling before the deposit site is reached. In contrast, simulations with a hidden magmatic intrusion beneath the Pirquitas deposit are in line with field observations, which include mineralized hydrothermal breccias in the deposit area.},
  language  = {en}
}
@phdthesis{Zali2023,
  author    = {Zali, Zahra},
  title     = {Volcanic tremor analysis based on advanced signal processing concepts including music information retrieval (MIR) strategies},
  doi       = {10.25932/publishup-61086},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610866},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 95},
  year      = {2023},
  abstract  = {Volcanoes are one of the Earth's most dynamic zones and responsible for many changes in our planet. Volcano seismology aims to provide an understanding of the physical processes in volcanic systems and anticipate the style and timing of eruptions by analyzing the seismic records. Volcanic tremor signals are usually observed in the seismic records before or during volcanic eruptions. Their analysis contributes to evaluate the evolving volcanic activity and potentially predict eruptions. Years of continuous seismic monitoring now provide useful information for operational eruption forecasting. The continuously growing amount of seismic recordings, however, poses a challenge for analysis, information extraction, and interpretation, to support timely decision making during volcanic crises. Furthermore, the complexity of eruption processes and precursory activities makes the analysis challenging. A challenge in studying seismic signals of volcanic origin is the coexistence of transient signal swarms and long-lasting volcanic tremor signals. Separating transient events from volcanic tremors can, therefore, contribute to improving our understanding of the underlying physical processes. Some similar issues (data reduction, source separation, extraction, and classification) are addressed in the context of music information retrieval (MIR). The signal characteristics of acoustic and seismic recordings comprise a number of similarities. This thesis is going beyond classical signal analysis techniques usually employed in seismology by exploiting similarities of seismic and acoustic signals and building the information retrieval strategy on the expertise developed in the field of MIR. First, inspired by the idea of harmonic-percussive separation (HPS) in musical signal processing, I have developed a method to extract harmonic volcanic tremor signals and to detect transient events from seismic recordings. This provides a clean tremor signal suitable for tremor investigation along with a characteristic function suitable for earthquake detection. Second, using HPS algorithms, I have developed a noise reduction technique for seismic signals. This method is especially useful for denoising ocean bottom seismometers, which are highly contaminated by noise. The advantage of this method compared to other denoising techniques is that it doesn't introduce distortion to the broadband earthquake waveforms, which makes it reliable for different applications in passive seismological analysis. Third, to address the challenge of extracting information from high-dimensional data and investigating the complex eruptive phases, I have developed an advanced machine learning model that results in a comprehensive signal processing scheme for volcanic tremors. Using this method seismic signatures of major eruptive phases can be automatically detected. This helps to provide a chronology of the volcanic system. Also, this model is capable to detect weak precursory volcanic tremors prior to the eruption, which could be used as an indicator of imminent eruptive activity. The extracted patterns of seismicity and their temporal variations finally provide an explanation for the transition mechanism between eruptive phases.},
  language  = {en}
}
@phdthesis{ErbelloDoelesso2023,
  author    = {Erbello Doelesso, Asfaw},
  title     = {Cenozoic magma-assisted continental rifting and crustal block rotations in an extensional overlap zone between two rift segments, Southwest Ethiopia, East Africa},
  doi       = {10.25932/publishup-61096},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610968},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 167},
  year      = {2023},
  abstract  = {Continental rifts are key geodynamic regions where the complex interplay of magmatism and faulting activity can be studied to understand the driving forces of extension and the formation of new divergent plate boundaries. Well-preserved rift morphology can provide a wealth of information on the growth, interaction, and linkage of normal-fault systems through time. If rift basins are preserved over longer geologic time periods, sedimentary archives generated during extensional processes may mirror tectonic and climatic influences on erosional and sedimentary processes that have varied over time. Rift basins are furthermore strategic areas for hydrocarbon and geothermal energy exploration, and they play a central role in species dispersal and evolution as well as providing or inhibiting hydrologic connectivity along basins at emerging plate boundaries. The Cenozoic East African rift system (EARS) is one of the most important continental extension zones, reflecting a range of evolutionary stages from an early rift stage with isolated basins in Malawi to an advanced stage of continental extension in southern Afar. Consequently, the EARS is an ideal natural laboratory that lends itself to the study of different stages in the breakup of a continent. The volcanically and seismically active eastern branch of the EARS is characterized by multiple, laterally offset tectonic and magmatic segments where adjacent extensional basins facilitate crustal extension either across a broad deformation zone or via major transfer faulting. The Broadly Rifted Zone (BRZ) in southern Ethiopia is an integral part of the eastern branch of the EARS; in this region, rift segments of the southern Ethiopian Rift (sMER) and northern Kenyan Rift (nKR) propagate in opposite directions in a region with one of the earliest manifestations of volcanism and extensional tectonism in East Africa. The basin margins of the Chew-Bahir Basin and the Gofa Province, characterized by a semi-arid climate and largely uniform lithology, provide ideal conditions for studying the tectonic and geomorphologic features of this complex kinematic transfer zone, but more importantly, this area is suitable for characterizing and quantifying the overlap between the propagating structures of the sMER and nKR and the resulting deformation patterns of the BRZ transfer zones. In this study, I have combined data from thermochronology, thermal modeling, morphometry, paleomagnetic analysis, geochronology, and geomorphological field observations with information from published studies to reconstruct the spatiotemporal relationship between volcanism and fault activity in the BRZ and quantify the deformation patterns of the overlapping rift segments. I present the following results: (1) new thermochronological data from the en-{\´e}chelon basin margins and footwall blocks of the rift flanks and morphometric results verified in the field to link different phases of magmatism and faulting during extension and infer geomorphological landscape features related to the current tectonic interaction between the nKR and the sMER; (2) temporally constrained paleomagnetic data from the BRZ overlap zone between the Ethiopian and Kenyan rifts to quantitatively determine block rotation between the two segments. Combining the collected data, time-temperature histories of thermal modeling results from representative samples show well-defined deformation phases between 25-20 Ma, 15-9Ma, and ~5 Ma to the present. Each deformation phase is characterized by the onset of rapid cooling (>2°C/Ma) of the crust associated with uplift or exhumation of the rift shoulder. After an initial, spatially very diffuse phase of extension, the rift has gradually evolved into a system of connected structures formed in an increasingly focused rift zone during the last 5 Ma. Regarding the morphometric analysis of the rift structures, it can be shown that normalized slope indices of the river courses, spatial arrangement of knickpoints in the river longitudinal profiles of the footwall blocks, local relief values, and the average maximum values of the slope of the river profiles indicate a gradual increase in the extension rate from north (Sawula basin: mature) to south (Chew Bahir: young). The complexity of the structural evolution of the BRZ overlap zone between nKR and sMER is further emphasized by the documentation of crustal blocks around a vertical axis. A comparison of the mean directions obtained for the Eo-Oligocene (Ds=352.6°, Is=-17.0°, N=18, α95=5.5°) and Miocene (Ds=2.9°, Is=0.9°, N=9, α95=12.4°) volcanics relative to the pole for stable South Africa and with respect to the corresponding ages of the analyzed units record a significant counterclockwise rotation of ~11.1°± 6.4° and insignificant CCW rotation of ~3.2° ± 11.5°, respectively.},
  language  = {en}
}
@phdthesis{Khawaja2023,
  author    = {Khawaja, Muhammad Asim},
  title     = {Improving earthquake forecast modeling and testing using the multi-resolution grids},
  school      = {Universit{\"a}t Potsdam},
  pages     = {107},
  year      = {2023},
  language  = {en}
}
@phdthesis{Freisleben2023,
  author    = {Freisleben, Roland},
  title     = {Deciphering the mechanisms of permanent forearc deformation based on marine terraces},
  doi       = {10.25932/publishup-61035},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610359},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiv, 153},
  year      = {2023},
  abstract  = {The Andes reflect Cenozoic deformation and uplift along the South American margin in the context of regional shortening associated with the interaction between the subducting Nazca plate and the overriding continental South American plate. Simultaneously, multiple levels of uplifted marine terraces constitute laterally continuous geomorphic features related to the accumulation of permanent forearc deformation in the coastal realm. However, the mechanisms responsible for permanent coastal uplift and the persistency of current/decadal deformation patterns over millennial timescales are still not fully understood. This dissertation presents a continental-scale database of last interglacial terrace elevations and uplift rates along the South American coast that provides the basis for an analysis of a variety of mechanisms that are possibly responsible for the accumulation of permanent coastal uplift. Regional-scale mapping and analysis of multiple, late Pleistocene terrace levels in central Chile furthermore provide valuable insights regarding the persistency of current seismic asperities, the role of upper-plate faulting, and the impact of bathymetric ridges on permanent forearc deformation. The database of last interglacial terrace elevations reveals an almost continuous signal of background-uplift rates along the South American coast at ~0.22 mm/yr that is modified by various short- to long-wavelength changes. Spatial correlations with crustal faults and subducted bathymetric ridges suggest long-term deformation to be affected by these features, while the latitudinal variability of climate forcing factors has a profound impact on the generation and preservation of marine terraces. Systematic wavelength analyses and comparisons of the terrace-uplift rate signal with different tectonic parameters reveal short-wavelength deformation to result from crustal faulting, while intermediate- to long-wavelength deformation might indicate various extents of long-term seismotectonic segments on the megathrust, which are at least partially controlled by the subduction of bathymetric anomalies. The observed signal of background-uplift rate is likely accumulated by moderate earthquakes near the Moho, suggesting multiple, spatiotemporally distinct phases of uplift that manifest as a continuous uplift signal over millennial timescales. Various levels of late Pleistocene marine terraces in the 2015 M8.3 Illapel-earthquake area reveal a range of uplift rates between 0.1 and 0.6 mm/yr and indicate decreasing uplift rates since ~400 ka. These glacial-cycle uplift rates do not correlate with current or decadal estimates of coastal deformation suggesting seismic asperities not to be persistent features on the megathrust that control the accumulation of permanent forearc deformation over long timescales of 105 years. Trench-parallel, crustal normal faults modulate the characteristics of permanent forearc-deformation; upper-plate extension likely represents a second-order phenomenon resulting from subduction erosion and subsequent underplating that lead to regional tectonic uplift and local gravitational collapse of the forearc. In addition, variable activity with respect to the subduction of the Juan Fern{\´a}ndez Ridge can be detected in the upper plate over the course of multiple interglacial periods, emphasizing the role of bathymetric anomalies in causing local increases in terrace-uplift rate. This thesis therefore provides new insights into the current understanding of subduction-zone processes and the dynamics of coastal forearc deformation, whose different interacting forcing factors impact the topographic and geomorphic evolution of the western South American coast.},
  language  = {en}
}
@phdthesis{Mester2023,
  author    = {Mester, Benedikt},
  title     = {Modeling flood-induced human displacement risk under global change},
  doi       = {10.25932/publishup-60929},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-609293},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 143},
  year      = {2023},
  abstract  = {Extreme flooding displaces an average of 12 million people every year. Marginalized populations in low-income countries are in particular at high risk, but also industrialized countries are susceptible to displacement and its inherent societal impacts. The risk of being displaced results from a complex interaction of flood hazard, population exposed in the floodplains, and socio-economic vulnerability. Ongoing global warming changes the intensity, frequency, and duration of flood hazards, undermining existing protection measures. Meanwhile, settlements in attractive yet hazardous flood-prone areas have led to a higher degree of population exposure. Finally, the vulnerability to displacement is altered by demographic and social change, shifting economic power, urbanization, and technological development. These risk components have been investigated intensively in the context of loss of life and economic damage, however, only little is known about the risk of displacement under global change. This thesis aims to improve our understanding of flood-induced displacement risk under global climate change and socio-economic change. This objective is tackled by addressing the following three research questions. First, by focusing on the choice of input data, how well can a global flood modeling chain reproduce flood hazards of historic events that lead to displacement? Second, what are the socio-economic characteristics that shape the vulnerability to displacement? Finally, to what degree has climate change potentially contributed to recent flood-induced displacement events? To answer the first question, a global flood modeling chain is evaluated by comparing simulated flood extent with satellite-derived inundation information for eight major flood events. A focus is set on the sensitivity to different combinations of the underlying climate reanalysis datasets and global hydrological models which serve as an input for the global hydraulic model. An evaluation scheme of performance scores shows that simulated flood extent is mostly overestimated without the consideration of flood protection and only for a few events dependent on the choice of global hydrological models. Results are more sensitive to the underlying climate forcing, with two datasets differing substantially from a third one. In contrast, the incorporation of flood protection standards results in an underestimation of flood extent, pointing to potential deficiencies in the protection level estimates or the flood frequency distribution within the modeling chain. Following the analysis of a physical flood hazard model, the socio-economic drivers of vulnerability to displacement are investigated in the next step. For this purpose, a satellite- based, global collection of flood footprints is linked with two disaster inventories to match societal impacts with the corresponding flood hazard. For each event the number of affected population, assets, and critical infrastructure, as well as socio-economic indicators are computed. The resulting datasets are made publicly available and contain 335 displacement events and 695 mortality/damage events. Based on this new data product, event-specific displacement vulnerabilities are determined and multiple (national) dependencies with the socio-economic predictors are derived. The results suggest that economic prosperity only partially shapes vulnerability to displacement; urbanization, infant mortality rate, the share of elderly, population density and critical infrastructure exhibit a stronger functional relationship, suggesting that higher levels of development are generally associated with lower vulnerability. Besides examining the contextual drivers of vulnerability, the role of climate change in the context of human displacement is also being explored. An impact attribution approach is applied on the example of Cyclone Idai and associated extreme coastal flooding in Mozambique. A combination of coastal flood modeling and satellite imagery is used to construct factual and counterfactual flood events. This storyline-type attribution method allows investigating the isolated or combined effects of sea level rise and the intensification of cyclone wind speeds on coastal flooding. The results suggest that displacement risk has increased by 3.1 to 3.5\% due to the total effects of climate change on coastal flooding, with the effects of increasing wind speed being the dominant factor. In conclusion, this thesis highlights the potentials and challenges of modeling flood- induced displacement risk. While this work explores the sensitivity of global flood modeling to the choice of input data, new questions arise on how to effectively improve the reproduction of flood return periods and the representation of protection levels. It is also demonstrated that disentangling displacement vulnerabilities is feasible, with the results providing useful information for risk assessments, effective humanitarian aid, and disaster relief. The impact attribution study is a first step in assessing the effects of global warming on displacement risk, leading to new research challenges, e.g., coupling fluvial and coastal flood models or the attribution of other hazard types and displacement events. This thesis is one of the first to address flood-induced displacement risk from a global perspective. The findings motivate for further development of the global flood modeling chain to improve our understanding of displacement vulnerability and the effects of global warming.},
  language  = {en}
}
@phdthesis{Kudriavtseva2023,
  author    = {Kudriavtseva, Anna},
  title     = {Interactions between tectonics, climate, and surface processes in the Kyrgyz Tian Shan},
  doi       = {10.25932/publishup-60372},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-603728},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XV, 164},
  year      = {2023},
  abstract  = {During the Cenozoic, global cooling and uplift of the Tian Shan, Pamir, and Tibetan plateau modified atmospheric circulation and reduced moisture supply to Central Asia. These changes led to aridification in the region during the Neogene. Afterwards, Quaternary glaciations led to modification of the landscape and runoff. In the Issyk-Kul basin of the Kyrgyz Tian Shan, the sedimentary sequences reflect the development of the adjacent ranges and local climatic conditions. In this work, I reconstruct the late Miocene - early Pleistocene depositional environment, climate, and lake development in the Issyk-Kul basin using facies analyses and stable δ18O and δ13C isotopic records from sedimentary sections dated by magnetostratigraphy and 26Al/10Be isochron burial dating. Also, I present 10Be-derived millennial-scale modern and paleo-denudation rates from across the Kyrgyz Tian Shan and long-term exhumation rates calculated from published thermochronology data. This allows me to examine spatial and temporal changes in surface processes in the Kyrgyz Tian Shan. In the Issyk-Kul basin, the style of fluvial deposition changed at ca. 7 Ma, and aridification in the basin commenced concurrently, as shown by magnetostratigraphy and the δ18O and δ13C data. Lake formation commenced on the southern side of the basin at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. 26Al/10Be isochron burial dating and paleocurrent analysis show that the Kungey range to the north of the basin grew eastward, leading to a change from fluvial-alluvial deposits to proximal alluvial fan conglomerates at 5-4 Ma in the easternmost part of the basin. This transition occurred at 2.6-2.8 Ma on the southern side of the basin, synchronously with the intensification of the Northern Hemisphere glaciation. The paleo-denudation rates from 2.7-2.0 Ma are as low as long-term exhumation rates, and only the millennial-scale denudation rates record an acceleration of denudation. This work concludes that the growth of the ranges to the north of the basin led to creation of the topographic barrier at ca. 7 Ma and a subsequent aridification in the Issyk-Kul basin. Increased subsidence and local tectonically-induced river system reorganization on the southern side of the basin enabled lake formation at ca. 5 Ma, while growth of the Kungey range blocked westward-draining rivers and led to sediment starvation and lake expansion. Denudational response of the Kyrgyz Tian Shan landscape is delayed due to aridity and only substantial cooling during the late Quaternary glacial cycles led to notable acceleration of denudation. Currently, increased glacier reduction and runoff controls a more rapid denudation of the northern slope of the Terskey range compared to other ranges of the Kyrgyz Tian Shan.},
  language  = {en}
}
@phdthesis{Reich2023,
  author    = {Reich, Marvin},
  title     = {Advances in hydrogravimetry},
  doi       = {10.25932/publishup-60479},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-604794},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 142},
  year      = {2023},
  abstract  = {The interest of the hydrological community in the gravimetric method has steadily increased within the last decade. This is reflected by numerous studies from many different groups with a broad range of approaches and foci. Many of those are traditionally rather hydrology-oriented groups who recognized gravimetry as a potential added value for their hydrological investigations. While this resulted in a variety of interesting and useful findings, contributing to extend the respective knowledge and confirming the methodological potential, on the other hand, many interesting and unresolved questions emerged. This thesis manifests efforts, analyses and solutions carried out in this regard. Addressing and evaluating many of those unresolved questions, the research contributes to advancing hydrogravimetry, the combination of gravimetric and hydrological methods, in showing how gravimeters are a highly useful tool for applied hydrological field research. In the first part of the thesis, traditional setups of stationary terrestrial superconducting gravimeters are addressed. They are commonly installed within a dedicated building, the impermeable structure of which shields the underlying soil from natural exchange of water masses (infiltration, evapotranspiration, groundwater recharge). As gravimeters are most sensitive to mass changes directly beneath the meter, this could impede their suitability for local hydrological process investigations, especially for near-surface water storage changes (WSC). By studying temporal local hydrological dynamics at a dedicated site equipped with traditional hydrological measurement devices, both below and next to the building, the impact of these absent natural dynamics on the gravity observations were quantified. A comprehensive analysis with both a data-based and model-based approach led to the development of an alternative method for dealing with this limitation. Based on determinable parameters, this approach can be transferred to a broad range of measurement sites where gravimeters are deployed in similar structures. Furthermore, the extensive considerations on this topic enabled a more profound understanding of this so called umbrella effect. The second part of the thesis is a pilot study about the field deployment of a superconducting gravimeter. A newly developed field enclosure for this gravimeter was tested in an outdoor installation adjacent to the building used to investigate the umbrella effect. Analyzing and comparing the gravity observations from both indoor and outdoor gravimeters showed performance with respect to noise and stable environmental conditions was equivalent while the sensitivity to near-surface WSC was highly increased for the field deployed instrument. Furthermore it was demonstrated that the latter setup showed gravity changes independent of the depth where mass changes occurred, given their sufficiently wide horizontal extent. As a consequence, the field setup suits monitoring of WSC for both short and longer time periods much better. Based on a coupled data-modeling approach, its gravity time series was successfully used to infer and quantify local water budget components (evapotranspiration, lateral subsurface discharge) on the daily to annual time scale. The third part of the thesis applies data from a gravimeter field deployment for applied hydrological process investigations. To this end, again at the same site, a sprinkling experiment was conducted in a 15 x 15 m area around the gravimeter. A simple hydro-gravimetric model was developed for calculating the gravity response resulting from water redistribution in the subsurface. It was found that, from a theoretical point of view, different subsurface water distribution processes (macro pore flow, preferential flow, wetting front advancement, bypass flow and perched water table rise) lead to a characteristic shape of their resulting gravity response curve. Although by using this approach it was possible to identify a dominating subsurface water distribution process for this site, some clear limitations stood out. Despite the advantage for field installations that gravimetry is a non-invasive and integral method, the problem of non-uniqueness could only be overcome by additional measurements (soil moisture, electric resistivity tomography) within a joint evaluation. Furthermore, the simple hydrological model was efficient for theoretical considerations but lacked the capability to resolve some heterogeneous spatial structures of water distribution up to a needed scale. Nevertheless, this unique setup for plot to small scale hydrological process research underlines the high potential of gravimetery and the benefit of a field deployment. The fourth and last part is dedicated to the evaluation of potential uncertainties arising from the processing of gravity observations. The gravimeter senses all mass variations in an integral way, with the gravitational attraction being directly proportional to the magnitude of the change and inversely proportional to the square of the distance of the change. Consequently, all gravity effects (for example, tides, atmosphere, non-tidal ocean loading, polar motion, global hydrology and local hydrology) are included in an aggregated manner. To isolate the signal components of interest for a particular investigation, all non-desired effects have to be removed from the observations. This process is called reduction. The large-scale effects (tides, atmosphere, non-tidal ocean loading and global hydrology) cannot be measured directly and global model data is used to describe and quantify each effect. Within the reduction process, model errors and uncertainties propagate into the residual, the result of the reduction. The focus of this part of the thesis is quantifying the resulting, propagated uncertainty for each individual correction. Different superconducting gravimeter installations were evaluated with respect to their topography, distance to the ocean and the climate regime. Furthermore, different time periods of aggregated gravity observation data were assessed, ranging from 1 hour up to 12 months. It was found that uncertainties were highest for a frequency of 6 months and smallest for hourly frequencies. Distance to the ocean influences the uncertainty of the non-tidal ocean loading component, while geographical latitude affects uncertainties of the global hydrological component. It is important to highlight that the resulting correction-induced uncertainties in the residual have the potential to mask the signal of interest, depending on the signal magnitude and its frequency. These findings can be used to assess the value of gravity data across a range of applications and geographic settings. In an overarching synthesis all results and findings are discussed with a general focus on their added value for bringing hydrogravimetric field research to a new level. The conceptual and applied methodological benefits for hydrological studies are highlighted. Within an outlook for future setups and study designs, it was once again shown what enormous potential is offered by gravimeters as hydrological field tools.},
  language  = {en}
}
@phdthesis{Pons2023,
  author    = {Pons, Micha{\"e}l},
  title     = {The Nature of the tectonic shortening in Central Andes},
  doi       = {10.25932/publishup-60089},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-600892},
  school      = {Universit{\"a}t Potsdam},
  pages     = {160},
  year      = {2023},
  abstract  = {The Andean Cordillera is a mountain range located at the western South American margin and is part of the Eastern- Circum-Pacific orogenic Belt. The ~7000 km long mountain range is one of the longest on Earth and hosts the second largest orogenic plateau in the world, the Altiplano-Puna plateau. The Andes are known as a non-collisional subduction-type orogen which developed as a result of the interaction between the subducted oceanic Nazca plate and the South American continental plate. The different Andean segments exhibit along-strike variations of morphotectonic provinces characterized by different elevations, volcanic activity, deformation styles, crustal thickness, shortening magnitude and oceanic plate geometry. Most of the present-day elevation can be explained by crustal shortening in the last ~50 Ma, with the shortening magnitude decreasing from ~300 km in the central (15°S-30°S) segment to less than half that in the southern part (30°S-40°S). Several factors were proposed that might control the magnitude and acceleration of shortening of the Central Andes in the last 15 Ma. One important factor is likely the slab geometry. At 27-33°S, the slab dips horizontally at ~100 km depth due to the subduction of the buoyant Juan Fernandez Ridge, forming the Pampean flat-slab. This horizontal subduction is thought to influence the thermo-mechanical state of the Sierras Pampeanas foreland, for instance, by strengthening the lithosphere and promoting the thick-skinned propagation of deformation to the east, resulting in the uplift of the Sierras Pampeanas basement blocks. The flat-slab has migrated southwards from the Altiplano latitude at ~30 Ma to its present-day position and the processes and consequences associated to its passage on the contemporaneous acceleration of the shortening rate in Central Andes remain unclear. Although the passage of the flat-slab could offer an explanation to the acceleration of the shortening, the timing does not explain the two pulses of shortening at about 15 Ma and 4 Ma that are suggested from geological observations. I hypothesize that deformation in the Central Andes is controlled by a complex interaction between the subduction dynamics of the Nazca plate and the dynamic strengthening and weakening of the South American plate due to several upper plate processes. To test this hypothesis, a detailed investigation into the role of the flat-slab, the structural inheritance of the continental plate, and the subduction dynamics in the Andes is needed. Therefore, I have built two classes of numerical thermo-mechanical models: (i) The first class of models are a series of generic E-W-oriented high-resolution 2D subduction models thatinclude flat subduction in order to investigate the role of the subduction dynamics on the temporal variability of the shortening rate in the Central Andes at Altiplano latitudes (~21°S). The shortening rate from the models was then validated with the observed tectonic shortening rate in the Central Andes. (ii) The second class of models are a series of 3D data-driven models of the present-day Pampean flat-slab configuration and the Sierras Pampeanas (26-42°S). The models aim to investigate the relative contribution of the present-day flat subduction and inherited structures in the continental lithosphere on the strain localization. Both model classes were built using the advanced finite element geodynamic code ASPECT. The first main finding of this work is to suggest that the temporal variability of shortening in the Central Andes is primarily controlled by the subduction dynamics of the Nazca plate while it penetrates into the mantle transition zone. These dynamics depends on the westward velocity of the South American plate that provides the main crustal shortening force to the Andes and forces the trench to retreat. When the subducting plate reaches the lower mantle, it buckles on it-self until the forced trench retreat causes the slab to steepen in the upper mantle in contrast with the classical slab-anchoring model. The steepening of the slab hinders the trench causing it to resist the advancing South American plate, resulting in the pulsatile shortening. This buckling and steepening subduction regime could have been initiated because of the overall decrease in the westwards velocity of the South American plate. In addition, the passage of the flat-slab is required to promote the shortening of the continental plate because flat subduction scrapes the mantle lithosphere, thus weakening the continental plate. This process contributes to the efficient shortening when the trench is hindered, followed by mantle lithosphere delamination at ~20 Ma. Finally, the underthrusting of the Brazilian cratonic shield beneath the orogen occurs at ~11 Ma due to the mechanical weakening of the thick sediments covered the shield margin, and due to the decreasing resistance of the weakened lithosphere of the orogen. The second main finding of this work is to suggest that the cold flat-slab strengthens the overriding continental lithosphere and prevents strain localization. Therefore, the deformation is transmitted to the eastern front of the flat-slab segment by the shear stress operating at the subduction interface, thus the flat-slab acts like an indenter that "bulldozes" the mantle-keel of the continental lithosphere. The offset in the propagation of deformation to the east between the flat and steeper slab segments in the south causes the formation of a transpressive dextral shear zone. Here, inherited faults of past tectonic events are reactivated and further localize the deformation in an en-echelon strike-slip shear zone, through a mechanism that I refer to as "flat-slab conveyor". Specifically, the shallowing of the flat-slab causes the lateral deformation, which explains the timing of multiple geological events preceding the arrival of the flat-slab at 33°S. These include the onset of the compression and of the transition between thin to thick-skinned deformation styles resulting from the crustal contraction of the crust in the Sierras Pampeanas some 10 and 6 Myr before the Juan Fernandez Ridge collision at that latitude, respectively.},
  language  = {en}
}
@phdthesis{Illien2023,
  author    = {Illien, Luc},
  title     = {Time-dependent properties of the shallow subsurface},
  doi       = {10.25932/publishup-59936},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-599367},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xviii, 133},
  year      = {2023},
  abstract  = {The shallow Earth's layers are at the interplay of many physical processes: some being driven by atmospheric forcing (precipitation, temperature...) whereas others take their origins at depth, for instance ground shaking due to seismic activity. These forcings cause the subsurface to continuously change its mechanical properties, therefore modulating the strength of the surface geomaterials and hydrological fluxes. Because our societies settle and rely on the layers hosting these time-dependent properties, constraining the hydro-mechanical dynamics of the shallow subsurface is crucial for our future geographical development. One way to investigate the ever-changing physical changes occurring under our feet is through the inference of seismic velocity changes from ambient noise, a technique called seismic interferometry. In this dissertation, I use this method to monitor the evolution of groundwater storage and damage induced by earthquakes. Two research lines are investigated that comprise the key controls of groundwater recharge in steep landscapes and the predictability and duration of the transient physical properties due to earthquake ground shaking. These two types of dynamics modulate each other and influence the velocity changes in ways that are challenging to disentangle. A part of my doctoral research also addresses this interaction. Seismic data from a range of field settings spanning several climatic conditions (wet to arid climate) in various seismic-prone areas are considered. I constrain the obtained seismic velocity time-series using simple physical models, independent dataset, geophysical tools and nonlinear analysis. Additionally, a methodological development is proposed to improve the time-resolution of passive seismic monitoring.},
  language  = {en}
}
@phdthesis{Libon2023,
  author    = {Libon, L{\´e}lia},
  title     = {Stability of magnesite in the Earth lower mantle: insight from high-pressure and high-temperature experiments},
  doi       = {10.25932/publishup-60461},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-604616},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 114, xvi},
  year      = {2023},
  abstract  = {Carbonates carried in subducting slabs may play a major role in sourcing and storing carbon in the deep Earth's interior. Current estimates indicate that between 40 to 66 million tons of carbon per year enter subduction zones, but it is uncertain how much of it reaches the lower mantle. It appears that most of this carbon might be extracted from subducting slabs at the mantle wedge and only a limited amount continues deeper and eventually reaches the deep mantle. However, estimations on deeply subducted carbon broadly range from 0.0001 to 52 million tons of carbon per year. This disparity is primarily due to the limited understanding of the survival of carbonate minerals during their transport to deep mantle conditions. Indeed, carbon has very low solubility in mantle silicates, therefore it is expected to be stored primarily in accessory phases such as carbonates. Among those carbonates, magnesite (MgCO3), as a single phase, is the most stable under all mantle conditions. However, experimental investigation on the stability of magnesite in contact with SiO2 at lower mantle conditions suggests that magnesite is stable only along a cold subducted slab geotherm. Furthermore, our understanding of magnesite's stability when interacting with more complex mantle silicate phases remains incomplete. In the first part of this dissertation, laser-heated diamond anvil cells and multi-anvil apparatus experiments were performed to investigate the stability of magnesite in contact with iron-bearing mantle silicates. Sub-solidus reactions, melting, decarbonation and diamond formation were examined from shallow to mid-lower mantle conditions (25 to 68 GPa; 1300 to 2000 K). Multi-anvil experiments at 25 GPa show the formation of carbonate-rich melt, bridgmanite, and stishovite with melting occurring at a temperature corresponding to all geotherms except the coldest one. In situ X-ray diffraction, in laser-heating diamond anvil cells experiments, shows crystallization of bridgmanite and stishovite but no melt phase was detected in situ at high temperatures. To detect decarbonation phases such as diamond, Raman spectroscopy was used. Crystallization of diamonds is observed as a sub-solidus process even at temperatures relevant and lower than the coldest slab geotherm (1350 K at 33 GPa). Data obtained from this work suggest that magnesite is unstable in contact with the surrounding peridotite mantle in the upper-most lower mantle. The presence of magnesite instead induces melting under oxidized conditions and/or foster diamond formation under more reduced conditions, at depths ∼700 km. Consequently, carbonates will be removed from the carbonate-rich slabs at shallow lower mantle conditions, where subducted slabs can stagnate. Therefore, the transport of carbonate to deeper depths will be restricted, supporting the presence of a barrier for carbon subduction at the top of the lower mantle. Moreover, the reduction of magnesite, forming diamonds provides additional evidence that super-deep diamond crystallization is related to the reduction of carbonates or carbonated-rich melt. The second part of this dissertation presents the development of a portable laser-heating system optimized for X-ray emission spectroscopy (XES) or nuclear inelastic scattering (NIS) spectroscopy with signal collection at near 90◦. The laser-heated diamond anvil cell is the only static pressure device that can replicate the pressure and temperatures of the Earth's lower mantle and core. The high temperatures are reached by using high-powered lasers focused on the sample contained between the diamond anvils. Moreover, diamonds' transparency to X-rays enables in situ X-ray spectroscopy measurements that can probe the sample under high-temperature and high-pressure conditions. Therefore, the development of portable laser-heating systems has linked high-pressure and temperature research with high-resolution X-ray spectroscopy techniques to synchrotron beamlines that do not have a dedicated, permanent, laser-heating system. A general description of the system is provided, as well as details on the use of a parabolic mirror as a reflective imaging objective for on-axis laser heating and radiospectrometric temperature measurements with zero attenuation of incoming X-rays. The parabolic mirror improves the accuracy of temperature measurements free from chromatic aberrations in a wide spectral range and its perforation permits in situ X-rays measurement at synchrotron facilities. The parabolic mirror is a well-suited alternative to refractive objectives in laser heating systems, which will facilitate future applications in the use of CO2 lasers.},
  language  = {en}
}
@phdthesis{Li2023,
  author    = {Li, Zhen},
  title     = {Formation of Sub-Permafrost Methane Hydrate Reproduced by Numerical Modeling},
  doi       = {10.25932/publishup-60330},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-603302},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 109},
  year      = {2023},
  abstract  = {Natural gas hydrates are ice-like crystalline compounds containing water cavities that trap natural gas molecules like methane (CH4), which is a potent greenhouse gas with high energy density. The Mallik site at the Mackenzie Delta in the Canadian Arctic contains a large volume of technically recoverable CH4 hydrate beneath the base of the permafrost. Understanding how the sub-permafrost hydrate is distributed can aid in searching for the ideal locations for deploying CH4 production wells to develop the hydrate as a cleaner alternative to crude oil or coal. Globally, atmospheric warming driving permafrost thaw results in sub-permafrost hydrate dissociation, releasing CH4 into the atmosphere to intensify global warming. It is therefore crucial to evaluate the potential risk of hydrate dissociation due to permafrost degradation. To quantitatively predict hydrate distribution and volume in complex sub-permafrost environments, a numerical framework was developed to simulate sub-permafrost hydrate formation by coupling the equilibrium CH4-hydrate formation approach with a fluid flow and transport simulator (TRANSPORTSE). In addition, integrating the equations of state describing ice melting and forming with TRANSPORTSE enabled this framework to simulate the permafrost evolution during the sub-permafrost hydrate formation. A modified sub-permafrost hydrate formation mechanism for the Mallik site is presented in this study. According to this mechanism, the CH4-rich fluids have been vertically transported since the Late Pleistocene from deep overpressurized zones via geologic fault networks to form the observed hydrate deposits in the Kugmallit-Mackenzie Bay Sequences. The established numerical framework was verified by a benchmark of hydrate formation via dissolved methane. Model calibration was performed based on laboratory data measured during a multi-stage hydrate formation experiment undertaken in the LArge scale Reservoir Simulator (LARS). As the temporal and spatial evolution of simulated and observed hydrate saturation matched well, the LARS model was therefore validated. This laboratory-scale model was then upscaled to a field-scale 2D model generated from a seismic transect across the Mallik site. The simulation confirmed the feasibility of the introduced sub-permafrost hydrate formation mechanism by demonstrating consistency with field observations. The 2D model was extended to the first 3D model of the Mallik site by using well-logs and seismic profiles, to investigate the geologic controls on the spatial hydrate distribution. An assessment of this simulation revealed the hydraulic contribution of each geological element, including relevant fault networks and sedimentary sequences. Based on the simulation results, the observed heterogeneous distribution of sub-permafrost hydrate resulted from the combined factors of the source-gas generation rate, subsurface temperature, and the permeability of geologic elements. Analysis of the results revealed that the Mallik permafrost was heated by 0.8-1.3 °C, induced by the global temperature increase of 0.44 °C and accelerated by Arctic amplification from the early 1970s to the mid-2000s. This study presents a numerical framework that can be applied to study the formation of the permafrost-hydrate system from laboratory to field scales, across timescales ranging from hours to millions of years. Overall, these simulations deepen the knowledge about the dominant factors controlling the spatial hydrate distribution in sub-permafrost environments with heterogeneous geologic elements. The framework can support improving the design of hydrate formation experiments and provide valuable contributions to future industrial hydrate exploration and exploitation activities.},
  language  = {en}
}
@phdthesis{Olivotos2023,
  author    = {Olivotos, Spyros-Christos},
  title     = {Reconstructing the Landscape Evolution of South Central Africa by Surface Exposure Dating of Waterfalls},
  doi       = {10.25932/publishup-60169},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-601699},
  school      = {Universit{\"a}t Potsdam},
  pages     = {159},
  year      = {2023},
  abstract  = {The East African Rift System (EARS) is a significant example of active tectonics, which provides opportunities to examine the stages of continental faulting and landscape evolution. The southwest extension of the EARS is one of the most significant examples of active tectonics nowadays, however, seismotectonic research in the area has been scarce, despite the fundamental importance of neotectonics. Our first study area is located between the Northern Province of Zambia and the southeastern Katanga Province of the Democratic Republic of Congo. Lakes Mweru and Mweru Wantipa are part of the southwest extension of the EARS. Fault analysis reveals that, since the Miocene, movements along the active Mweru-Mweru Wantipa Fault System (MMFS) have been largely responsible for the reorganization of the landscape and the drainage patterns across the southwestern branch of the EARS. To investigate the spatial and temporal patterns of fluvial-lacustrine landscape development, we determined in-situ cosmogenic 10Be and 26Al in a total of twenty-six quartzitic bedrock samples that were collected from knickpoints across the Mporokoso Plateau (south of Lake Mweru) and the eastern part of the Kundelungu Plateau (north of Lake Mweru). Samples from the Mporokoso Plateau and close to the MMFS provide evidence of temporary burial. By contrast, surfaces located far from the MMFS appear to have remained uncovered since their initial exposure as they show consistent 10Be and 26Al exposure ages ranging up to ~830 ka. Reconciliation of the observed burial patterns with morphotectonic and stratigraphic analysis reveals the existence of an extensive paleo-lake during the Pleistocene. Through hypsometric analyses of the dated knickpoints, the potential maximum water level of the paleo-lake is constrained to ~1200 m asl (present lake lavel: 917 m asl). High denudation rates (up to ~40 mm ka-1) along the eastern Kundelungu Plateau suggest that footwall uplift, resulting from normal faulting, caused river incision, possibly controlling paleo-lake drainage. The lake level was reduced gradually reaching its current level at ~350 ka. Parallel to the MMFS in the north, the Upemba Fault System (UFS) extends across the southeastern Katanga Province of the Democratic Republic of Congo. This part of our research is focused on the geomorphological behavior of the Kiubo Waterfalls. The waterfalls are the currently active knickpoint of the Lufira River, which flows into the Upemba Depression. Eleven bedrock samples along the Lufira River and its tributary stream, Luvilombo River, were collected. In-situ cosmogenic 10Be and 26Al were used in order to constrain the K constant of the Stream Power Law equation. Constraining the K constant allowed us to calculate the knickpoint retreat rate of the Kiubo Waterfalls at ~0.096 m a-1. Combining the calculated retreat rate of the knickpoint with DNA sequencing from fish populations, we managed to present extrapolation models and estimate the location of the onset of the Kiubo Waterfalls, revealing its connection to the seismicity of the UFS.},
  language  = {en}
}
@phdthesis{Rembe2023,
  author    = {Rembe, Johannes},
  title     = {Hercynian to Eocimmerian evolution of the North Pamir in Central Asia},
  doi       = {10.25932/publishup-59751},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-597510},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxvi, 154, CX},
  year      = {2023},
  abstract  = {The North Pamir, part of the India-Asia collision zone, essentially formed during the late Paleozoic to late Triassic-early Jurassic. Coeval to the subduction of the Turkestan ocean—during the Carboniferous Hercynian orogeny in the Tien Shan—a portion of the Paleo-Tethys ocean subducted northward and lead to the formation and obduction of a volcanic arc. This Carboniferous North Pamir arc is of Andean style in the western Darvaz segment and trends towards an intraoceanic arc in the eastern, Oytag segment. A suite of arc-volcanic rocks and intercalated, marine sediments together with intruded voluminous plagiogranites (trondhjemite and tonalite) and granodiorites was uplifted and eroded during the Permian, as demonstrated by widespread sedimentary unconformities. Today it constitutes a major portion of the North Pamir. In this work, the first comprehensive Uranium-Lead (U-Pb) laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) radiometric age data are presented along with geochemical data from the volcanic and plutonic rocks of the North Pamir volcanic arc. Zircon U-Pb data indicate a major intrusive phase between 340 and 320 Ma. The magmatic rocks show an arc-signature, with more primitive signatures in the Oytag segment compared to the Darvaz segment. Volcanic rocks in the Chinese North Pamir were indirectly dated by determining the age of ocean floor alteration. We investigate calcite filled vesicles and show that oxidative sea water and the basaltic host rock are major trace element sources. The age of ocean floor alteration, within a range of 25 Ma, constrains the extrusion age of the volcanic rocks. In the Chinese Pamir, arc-volcanic basalts have been dated to the Visean-Serpukhovian boundary. This relates the North Pamir volcanic arc to coeval units in the Tien Shan. Our findings further question the idea of a continuous Tarim-Tajik continent in the Paleozoic. From the Permian (Guadalupian) on, a progressive sea-retreat led to continental conditions in the northeastern Pamir. Large parts of Central Asia were affected by transcurrent tectonics, while subduction of the Paleo-Tethys went on south of the accreted North Pamir arc, likely forming an accretionary wedge, representing an early stage of the later Karakul-Mazar tectonic unit. Graben systems dissected the Permian carbonate platforms, that formed on top of the uplifted Carboniferous arc in the central and western North Pamir. A continental graben formed in the eastern North Pamir. Zircon U-Pb dating suggest initiation of volcanic activity at ~260 Ma. Extensional tectonics prevailed throughout the Triassic, forming the Hindukush-North Pamir rift system. New geochemistry and zircon U-Pb data tie volcanic rocks, found in the Chinese Pamir, to coeval arc-related plutonic rocks found within the Karakul-Mazar arc-accretionary complex. The sedimentary environment in the continental North Pamir rift evolved from an alluvial plain, lake dominated environment in the Guadalupian to a coarser-clastic, alluvial, braided river dominated in the Triassic. Volcanic activity terminated in the early Jurassic. We conducted Potassium-Argon (K-Ar) fine-fraction dating on the Shala Tala thrust fault, a major structure juxtaposing Paleozoic marine units of lower greenschist to amphibolite facies conditions against continental Permian deposits. Fault slip under epizonal conditions is dated to 204.8 ± 3.7 Ma (2σ), implying Rhaetian nappe emplacement. This pinpoints the Central-North Pamir collision, since the Shala Tala thrust was a back-thrust at that time.},
  language  = {en}
}
@phdthesis{Ribacki2023,
  author    = {Ribacki, Enrico},
  title     = {Intra-granitic pegmatites of the Las Chacras-Potrerillos batholith, Argentina},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVIII, 183},
  year      = {2023},
  language  = {en}
}
@phdthesis{GomezZapata2023,
  author    = {G{\´o}mez Zapata, Juan Camilo},
  title     = {Towards unifying approaches in exposure modelling for scenario-based multi-hazard risk assessments},
  doi       = {10.25932/publishup-58614},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-586140},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iii, xiii, 155},
  year      = {2023},
  abstract  = {This cumulative thesis presents a stepwise investigation of the exposure modelling process for risk assessment due to natural hazards while highlighting its, to date, not much-discussed importance and associated uncertainties. Although "exposure" refers to a very broad concept of everything (and everyone) that is susceptible to damage, in this thesis it is narrowed down to the modelling of large-area residential building stocks. Classical building exposure models for risk applications have been constructed fully relying on unverified expert elicitation over data sources (e.g., outdated census datasets), and hence have been implicitly assumed to be static in time and in space. Moreover, their spatial representation has also typically been simplified by geographically aggregating the inferred composition onto coarse administrative units whose boundaries do not always capture the spatial variability of the hazard intensities required for accurate risk assessments. These two shortcomings and the related epistemic uncertainties embedded within exposure models are tackled in the first three chapters of the thesis. The exposure composition of large-area residential building stocks is studied on the scope of scenario-based earthquake loss models. Then, the proposal of optimal spatial aggregation areas of exposure models for various hazard-related vulnerabilities is presented, focusing on ground-shaking and tsunami risks. Subsequently, once the experience is gained in the study of the composition and spatial aggregation of exposure for various hazards, this thesis moves towards a multi-hazard context while addressing cumulative damage and losses due to consecutive hazard scenarios. This is achieved by proposing a novel method to account for the pre-existing damage descriptions on building portfolios as a key input to account for scenario-based multi-risk assessment. Finally, this thesis shows how the integration of the aforementioned elements can be used in risk communication practices. This is done through a modular architecture based on the exploration of quantitative risk scenarios that are contrasted with social risk perceptions of the directly exposed communities to natural hazards. In Chapter 1, a Bayesian approach is proposed to update the prior assumptions on such composition (i.e., proportions per building typology). This is achieved by integrating high-quality real observations and then capturing the intrinsic probabilistic nature of the exposure model. Such observations are accounted as real evidence from both: field inspections (Chapter 2) and freely available data sources to update existing (but outdated) exposure models (Chapter 3). In these two chapters, earthquake scenarios with parametrised ground motion fields were transversally used to investigate the role of such epistemic uncertainties related to the exposure composition through sensitivity analyses. Parametrised scenarios of seismic ground shaking were the hazard input utilised to study the physical vulnerability of building portfolios. The second issue that was investigated, which refers to the spatial aggregation of building exposure models, was investigated within two decoupled vulnerability contexts: due to seismic ground shaking through the integration of remote sensing techniques (Chapter 3); and within a multi-hazard context by integrating the occurrence of associated tsunamis (Chapter 4). Therein, a careful selection of the spatial aggregation entities while pursuing computational efficiency and accuracy in the risk estimates due to such independent hazard scenarios (i.e., earthquake and tsunami) are discussed. Therefore, in this thesis, the physical vulnerability of large-area building portfolios due to tsunamis is considered through two main frames: considering and disregarding the interaction at the vulnerability level, through consecutive and decoupled hazard scenarios respectively, which were then contrasted. Contrary to Chapter 4, where no cumulative damages are addressed, in Chapter 5, data and approaches, which were already generated in former sections, are integrated with a novel modular method to ultimately study the likely interactions at the vulnerability level on building portfolios. This is tested by evaluating cumulative damages and losses after earthquakes with increasing magnitude followed by their respective tsunamis. Such a novel method is grounded on the possibility of re-using existing fragility models within a probabilistic framework. The same approach is followed in Chapter 6 to forecast the likely cumulative damages to be experienced by a building stock located in a volcanic multi-hazard setting (ash-fall and lahars). In that section, special focus was made on the manner the forecasted loss metrics are communicated to locally exposed communities. Co-existing quantitative scientific approaches (i.e., comprehensive exposure models; explorative risk scenarios involving single and multiple hazards) and semi-qualitative social risk perception (i.e., level of understanding that the exposed communities have about their own risk) were jointly considered. Such an integration ultimately allowed this thesis to also contribute to enhancing preparedness, science divulgation at the local level as well as technology transfer initiatives. Finally, a synthesis of this thesis along with some perspectives for improvement and future work are presented.},
  language  = {en}
}
@phdthesis{Zuhr2023,
  author    = {Zuhr, Alexandra},
  title     = {Proxy signal formation in palaeoclimate archives},
  doi       = {10.25932/publishup-58286},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-582864},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 167},
  year      = {2023},
  abstract  = {Throughout the last ~3 million years, the Earth's climate system was characterised by cycles of glacial and interglacial periods. The current warm period, the Holocene, is comparably stable and stands out from this long-term cyclicality. However, since the industrial revolution, the climate has been increasingly affected by a human-induced increase in greenhouse gas concentrations. While instrumental observations are used to describe changes over the past ~200 years, indirect observations via proxy data are the main source of information beyond this instrumental era. These data are indicators of past climatic conditions, stored in palaeoclimate archives around the Earth. The proxy signal is affected by processes independent of the prevailing climatic conditions. In particular, for sedimentary archives such as marine sediments and polar ice sheets, material may be redistributed during or after the initial deposition and subsequent formation of the archive. This leads to noise in the records challenging reliable reconstructions on local or short time scales. This dissertation characterises the initial deposition of the climatic signal and quantifies the resulting archive-internal heterogeneity and its influence on the observed proxy signal to improve the representativity and interpretation of climate reconstructions from marine sediments and ice cores. To this end, the horizontal and vertical variation in radiocarbon content of a box-core from the South China Sea is investigated. The three-dimensional resolution is used to quantify the true uncertainty in radiocarbon age estimates from planktonic foraminifera with an extensive sampling scheme, including different sample volumes and replicated measurements of batches of small and large numbers of specimen. An assessment on the variability stemming from sediment mixing by benthic organisms reveals strong internal heterogeneity. Hence, sediment mixing leads to substantial time uncertainty of proxy-based reconstructions with error terms two to five times larger than previously assumed. A second three-dimensional analysis of the upper snowpack provides insights into the heterogeneous signal deposition and imprint in snow and firn. A new study design which combines a structure-from-motion photogrammetry approach with two-dimensional isotopic data is performed at a study site in the accumulation zone of the Greenland Ice Sheet. The photogrammetry method reveals an intermittent character of snowfall, a layer-wise snow deposition with substantial contributions by wind-driven erosion and redistribution to the final spatially variable accumulation and illustrated the evolution of stratigraphic noise at the surface. The isotopic data show the preservation of stratigraphic noise within the upper firn column, leading to a spatially variable climate signal imprint and heterogeneous layer thicknesses. Additional post-depositional modifications due to snow-air exchange are also investigated, but without a conclusive quantification of the contribution to the final isotopic signature. Finally, this characterisation and quantification of the complex signal formation in marine sediments and polar ice contributes to a better understanding of the signal content in proxy data which is needed to assess the natural climate variability during the Holocene.},
  language  = {en}
}
@phdthesis{Tella2023,
  author    = {Tella, Timothy Oluwatobi},
  title     = {Exploring the roles of sediment production by Photozoan and Heterozoan biotas on the evolution of carbonate system geometries through forward modelling},
  doi       = {10.25932/publishup-58225},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-582257},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 123},
  year      = {2023},
  abstract  = {The role of biogenic carbonate producers in the evolution of the geometries of carbonate systems has been the subject of numerous research projects. Attempts to classify modern and ancient carbonate systems by their biotic components have led to the discrimination of biogenic carbonate producers broadly into Photozoans, which are characterised by an affinity for warm tropical waters and high dependence on light penetration, and Heterozoans which are generally associated with both cool water environments and nutrient-rich settings with little to no light penetration. These broad categories of carbonate sediment producers have also been recognised to dominate in specific carbonate systems. Photozoans are commonly dominant in flat-topped platforms with steep margins, while Heterozoans generally dominate carbonate ramps. However, comparatively little is known on how these two main groups of carbonate producers interact in the same system and impact depositional geometries responding to changes in environmental conditions such as sea level fluctuation, antecedent slope, sediment transport processes, etc. This thesis presents numerical models to investigate the evolution of Miocene carbonate systems in the Mediterranean from two shallow marine domains: 1) a Miocene flat-topped platform dominated by Photozoans, with a significant component of Hetrozoans in the slope and 2) a Heterozoan distally steepened ramp, with seagrass-influenced (Photozoan) inner ramp. The overarching aim of the three articles comprising this cumulative thesis is to provide a numerical study of the role of Photozoans and Heterozoans in the evolution of carbonate system geometries and how these biotas respond to changes in environmental conditions. This aim was achieved using stratigraphic forward modelling, which provides an approach to quantitatively integrate multi-scale datasets to reconstruct sedimentary processes and products during the evolution of a sedimentary system. In a Photozoan-dominated carbonate system, such as the Miocene Llucmajor platform in Western Mediterranean, stratigraphic forward modelling dovetailed with a robust set of sensitivity tests reveal how the geometry of the carbonate system is determined by the complex interaction of Heterozoan and Photozoan biotas in response to variable conditions of sea level fluctuation, substrate configuration, sediment transport processes and the dominance of Photozoan over Heterozoan production. This study provides an enhanced understanding of the different carbonate systems that are possible under different ecological and hydrodynamic conditions. The research also gives insight into the roles of different biotic associations in the evolution of carbonate geometries through time and space. The results further show that the main driver of platform progradation in a Llucmajor-type system is the lowstand production of Heterozoan sediments, which form the necessary substratum for Photozoan production. In Heterozoan systems, sediment production is mainly characterised by high transport deposits, that are prone to redistribution by waves and gravity, thereby precluding the development of steep margins. However, in the Menorca ramp, the occurrence of sediment trapping by seagrass led to the evolution of distal slope steepening. We investigated, through numerical modelling, how such a seagrass-influenced ramp responds to the frequency and amplitude of sea level changes, variable carbonate production between the euphotic and oligophotic zone, and changes in the configuration of the paleoslope. The study reinforces some previous hypotheses and presents alternative scenarios to the established concepts of high-transport ramp evolution. The results of sensitivity experiments show that steep slopes are favoured in ramps that develop in high-frequency sea level fluctuation with amplitudes between 20 m and 40 m. We also show that ramp profiles are significantly impacted by the paleoslope inclination, such that an optimal antecedent slope of about 0.15 degrees is required for the Menorca distally steepened ramp to develop. The third part presents an experimental case to argue for the existence of a Photozoan sediment threshold required for the development of steep margins in carbonate platforms. This was carried out by developing sensitivity tests on the forward models of the flat-topped (Llucmajor) platform and the distally steepened (Menorca) platform. The results show that models with Photozoan sediment proportion below a threshold of about 40\% are incapable of forming steep slopes. The study also demonstrates that though it is possible to develop steep margins by seagrass sediment trapping, such slopes can only be stabilized by the appropriate sediment fabric and/or microbial binding. In the Photozoan-dominated system, the magnitude of slope steepness depends on the proportion of Photozoan sediments in the system. Therefore, this study presents a novel tool for characterizing carbonate systems based on their biogenic components.},
  language  = {en}
}
@phdthesis{ArboledaZapata2023,
  author    = {Arboleda Zapata, Mauricio},
  title     = {Adapted inversion strategies for electrical resistivity data to explore layered near-surface environments},
  doi       = {10.25932/publishup-58135},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-581357},
  school      = {Universit{\"a}t Potsdam},
  pages     = {115},
  year      = {2023},
  abstract  = {The electrical resistivity tomography (ERT) method is widely used to investigate geological, geotechnical, and hydrogeological problems in inland and aquatic environments (i.e., lakes, rivers, and seas). The objective of the ERT method is to obtain reliable resistivity models of the subsurface that can be interpreted in terms of the subsurface structure and petrophysical properties. The reliability of the resulting resistivity models depends not only on the quality of the acquired data, but also on the employed inversion strategy. Inversion of ERT data results in multiple solutions that explain the measured data equally well. Typical inversion approaches rely on different deterministic (local) strategies that consider different smoothing and damping strategies to stabilize the inversion. However, such strategies suffer from the trade-off of smearing possible sharp subsurface interfaces separating layers with resistivity contrasts of up to several orders of magnitude. When prior information (e.g., from outcrops, boreholes, or other geophysical surveys) suggests sharp resistivity variations, it might be advantageous to adapt the parameterization and inversion strategies to obtain more stable and geologically reliable model solutions. Adaptations to traditional local inversions, for example, by using different structural and/or geostatistical constraints, may help to retrieve sharper model solutions. In addition, layer-based model parameterization in combination with local or global inversion approaches can be used to obtain models with sharp boundaries. In this thesis, I study three typical layered near-surface environments in which prior information is used to adapt 2D inversion strategies to favor layered model solutions. In cooperation with the coauthors of Chapters 2-4, I consider two general strategies. Our first approach uses a layer-based model parameterization and a well-established global inversion strategy to generate ensembles of model solutions and assess uncertainties related to the non-uniqueness of the inverse problem. We apply this method to invert ERT data sets collected in an inland coastal area of northern France (Chapter~2) and offshore of two Arctic regions (Chapter~3). Our second approach consists of using geostatistical regularizations with different correlation lengths. We apply this strategy to a more complex subsurface scenario on a local intermountain alluvial fan in southwestern Germany (Chapter~4). Overall, our inversion approaches allow us to obtain resistivity models that agree with the general geological understanding of the studied field sites. These strategies are rather general and can be applied to various geological environments where a layered subsurface structure is expected. The flexibility of our strategies allows adaptations to invert other kinds of geophysical data sets such as seismic refraction or electromagnetic induction methods, and could be considered for joint inversion approaches.},
  language  = {en}
}
@phdthesis{Klein2022,
  author    = {Klein, Konstantin Paul},
  title     = {Remote Sensing of Suspended Sediment Dynamics in the Arctic Nearshore Zone},
  doi       = {10.25932/publishup-57603},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-576032},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 85, xvii},
  year      = {2022},
  abstract  = {The Arctic nearshore zone plays a key role in the carbon cycle. Organic-rich sediments get eroded off permafrost affected coastlines and can be directly transferred to the nearshore zone. Permafrost in the Arctic stores a high amount of organic matter and is vulnerable to thermo-erosion, which is expected to increase due to climate change. This will likely result in higher sediment loads in nearshore waters and has the potential to alter local ecosystems by limiting light transmission into the water column, thus limiting primary production to the top-most part of it, and increasing nutrient export from coastal erosion. Greater organic matter input could result in the release of greenhouse gases to the atmosphere. Climate change also acts upon the fluvial system, leading to greater discharge to the nearshore zone. It leads to decreasing sea-ice cover as well, which will both increase wave energy and lengthen the open-water season. Yet, knowledge on these processes and the resulting impact on the nearshore zone is scarce, because access to and instrument deployment in the nearshore zone is challenging. Remote sensing can alleviate these issues in providing rapid data delivery in otherwise non-accessible areas. However, the waters in the Arctic nearshore zone are optically complex, with multiple influencing factors, such as organic rich suspended sediments, colored dissolved organic matter (cDOM), and phytoplankton. The goal of this dissertation was to use remotely sensed imagery to monitor processes related to turbidity caused by suspended sediments in the Arctic nearshore zone. In-situ measurements of water-leaving reflectance and surface water turbidity were used to calibrate a semi-empirical algorithm which relates turbidity from satellite imagery. Based on this algorithm and ancillary ocean and climate variables, the mechanisms underpinning nearshore turbidity in the Arctic were identified at a resolution not achieved before. The calibration of the Arctic Nearshore Turbidity Algorithm (ANTA) was based on in-situ measurements from the coastal and inner-shelf waters around Herschel Island Qikiqtaruk (HIQ) in the western Canadian Arctic from the summer seasons 2018 and 2019. It performed better than existing algorithms, developed for global applications, in relating turbidity from remotely sensed imagery. These existing algorithms were lacking validation data from permafrost affected waters, and were thus not able to reflect the complexity of Arctic nearshore waters. The ANTA has a higher sensitivity towards the lowest turbidity values, which is an asset for identifying sediment pathways in the nearshore zone. Its transferability to areas beyond HIQ was successfully demonstrated using turbidity measurements matching satellite image recordings from Adventfjorden, Svalbard. The ANTA is a powerful tool that provides robust turbidity estimations in a variety of Arctic nearshore environments. Drivers of nearshore turbidity in the Arctic were analyzed by combining ANTA results from the summer season 2019 from HIQ with ocean and climate variables obtained from the weather station at HIQ, the ERA5 reanalysis database, and the Mackenzie River discharge. ERA5 reanalysis data were obtained as domain averages over the Canadian Beaufort Shelf. Nearshore turbidity was linearly correlated to wind speed, significant wave height and wave period. Interestingly, nearshore turbidity was only correlated to wind speed at the shelf, but not to the in-situ measurements from the weather station at HIQ. This shows that nearshore turbidity, albeit being of limited spatial extent, gets influenced by the weather conditions multiple kilometers away, rather than in its direct vicinity. The large influence of wave energy on nearshore turbidity indicates that freshly eroded material off the coast is a major contributor to the nearshore sediment load. This contrasts results from the temperate and tropical oceans, where tides and currents are the major drivers of nearshore turbidity. The Mackenzie River discharge was not identified as a driver of nearshore turbidity in 2019, however, the analysis of 30 years of Landsat archive imagery from 1986 to 2016 suggests a direct link between the prevailing wind direction, which heavily influences the Mackenzie River plume extent, and nearshore turbidity around HIQ. This discrepancy could be caused by the abnormal discharge behavior of the Mackenzie River in 2019. This dissertation has substantially advanced the understanding of suspended sediment processes in the Arctic nearshore zone and provided new monitoring tools for future studies. The presented results will help to understand the role of the Arctic nearshore zone in the carbon cycle under a changing climate.},
  language  = {en}
}
@phdthesis{Patyniak2022,
  author    = {Patyniak, Magda},
  title     = {Seismotectonic segmentation, paleoearthquakes and style of deformation along the Northern Pamir thrust system, South Kyrgyzstan},
  doi       = {10.25932/publishup-57714},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-577141},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxii, 165},
  year      = {2022},
  abstract  = {The Pamir Frontal Thrust (PFT) located in the Trans Alai range in Central Asia is the principal active fault of the intracontinental India-Eurasia convergence zone and constitutes the northernmost boundary of the Pamir orogen at the NW edge of this collision zone. Frequent seismic activity and ongoing crustal shortening reflect the northward propagation of the Pamir into the intermontane Alai Valley. Quaternary deposits are being deformed and uplifted by the advancing thrust front of the Trans Alai range. The Alai Valley separates the Pamir range front from the Tien Shan mountains in the north; the Alai Valley is the vestige of a formerly contiguous basin that linked the Tadjik Depression in the west with the Tarim Basin in the east. GNSS measurements across the Central Pamir document a shortening rate of ~25 mm/yr, with a dramatic decrease of ~10-15 mm over a short distance across the northernmost Trans Alai range. This suggests that almost half of the shortening in the greater Pamir - Tien Shan collision zone is absorbed along the PFT. The short-term (geodetic) and long-term (geologic) shortening rates across the northern Pamir appear to be at odds with an apparent slip-rate discrepancy along the frontal fault system of the Pamir. Moreover, the present-day seismicity and historical records have not revealed great Mw > 7 earthquakes that might be expected with such a significant slip accommodation. In contrast, recent and historic earthquakes exhibit complex rupture patterns within and across seismotectonic segments bounding the Pamir mountain front, challenging our understanding of fault interaction and the seismogenic potential of this area, and leaving the relationships between seismicity and the geometry of the thrust front not well understood. In this dissertation I employ different approaches to assess the seismogenic behavior along the PFT. Firstly, I provide paleoseismic data from five trenches across the central PFT segment (cPFT) and compute a segment-wide earthquake chronology over the past 16 kyr. This novel dataset provides important insights into the recurrence, magnitude, and rupture extent of past earthquakes along the cPFT. I interpret five, possibly six paleoearthquakes that have ruptured the Pamir mountain front since ∼7 ka and 16 ka, respectively. My results indicate that at least three major earthquakes ruptured the full-segment length and possibly crossed segment boundaries with a recurrence interval of ∼1.9 kyr and potential magnitudes of up to Mw 7.4. Importantly, I did not find evidence for great (i.e., Mw ≥8) earthquakes. Secondly, I combine my paleoseimic results with morphometric analyses to establish a segment-wide distribution of the cumulative vertical separation along offset fluvial terraces and I model a long-term slip rate for the cPFT. My investigations reveal discrepancies between the extents of slip and rupture during apparent partial segment ruptures in the western half of the cPFT. Combined with significantly higher fault scarp offsets in this sector of the cPFT, the observations indicate a more mature fault section with a potential for future fault linkage. I estimate an average rate of horizontal motion for the cPFT of 4.1 ± 1.5 mm/yr during the past ∼5 kyr, which does not fully match the GNSS-derived present-day shortening rate of ∼10 mm/yr. This suggests a complex distribution of strain accumulation and potential slip partitioning between the cPFT and additional faults and folds within the Pamir that may be associated with a partially locked regional d{\´e}collement. The third part of the thesis provides new insights regarding the surface rupture of the 2008 Mw 6.6 Nura earthquake that ruptured along the eastern PFT sector. I explore this rupture in the context of its structural complexity by combining extensive field observations with high-resolution digital surface models. I provide a map of the rupture extent, net slip measurements, and updated regional geological observations. Based on this data I propose a tectonic model in this area associated with secondary flexural-slip faulting along steeply dipping bedding of folded Paleogene sedimentary strata that is related to deformation along a deeper blind thrust. Here, the strain release seems to be transferred from the PFT towards older inherited basement structures within the area of advanced Pamir-Tien Shan collision zone. The extensive research of my dissertation results in a paleoseismic database of the past 16 ~kyr, which contributes to the understanding of the seismogenic behavior of the PFT, but also to that of segmented thrust-fault systems in active collisional settings. My observations underscore the importance of combining different methodological approaches in the geosciences, especially in structurally complex tectonic settings like the northern Pamir. Discrepancy between GNSS-derived present-day deformation rates and those from different geological archives in the central part, as well as the widespread distribution of the deformation due to earthquake triggered strain transfer in the eastern part reveals the complexity of this collision zone and calls for future studies involving multi-temporal and interdisciplinary approaches.},
  language  = {en}
}
@phdthesis{Siegmund2022,
  author    = {Siegmund, Nicole},
  title     = {Wind driven soil particle uptake Quantifying drivers of wind erosion across the particle size spectrum},
  doi       = {10.25932/publishup-57489},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-574897},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 56},
  year      = {2022},
  abstract  = {Among the multitude of geomorphological processes, aeolian shaping processes are of special character, Pedogenic dust is one of the most important sources of atmospheric aerosols and therefore regarded as a key player for atmospheric processes. Soil dust emissions, being complex in composition and properties, influence atmospheric processes and air quality and has impacts on other ecosystems. In this because even though their immediate impact can be considered low (exceptions exist), their constant and large-scale force makes them a powerful player in the earth system. dissertation, we unravel a novel scientific understanding of this complex system based on a holistic dataset acquired during a series of field experiments on arable land in La Pampa, Argentina. The field experiments as well as the generated data provide information about topography, various soil parameters, the atmospheric dynamics in the very lower atmosphere (4m height) as well as measurements regarding aeolian particle movement across a wide range of particle size classes between 0.2μm up to the coarse sand. The investigations focus on three topics: (a) the effects of low-scale landscape structures on aeolian transport processes of the coarse particle fraction, (b) the horizontal and vertical fluxes of the very fine particles and (c) the impact of wind gusts on particle emissions. Among other considerations presented in this thesis, it could in particular be shown, that even though the small-scale topology does have a clear impact on erosion and deposition patterns, also physical soil parameters need to be taken into account for a robust statistical modelling of the latter. Furthermore, specifically the vertical fluxes of particulate matter have different characteristics for the particle size classes. Finally, a novel statistical measure was introduced to quantify the impact of wind gusts on the particle uptake and its application on the provided data set. The aforementioned measure shows significantly increased particle concentrations during points in time defined as gust event. With its holistic approach, this thesis further contributes to the fundamental understanding of how atmosphere and pedosphere are intertwined and affect each other.},
  language  = {en}
}
@phdthesis{DokhtDolatabadiEsfahani2022,
  author    = {Dokht Dolatabadi Esfahani, Reza},
  title     = {Time-dependent monitoring of near-surface and ground motion modelling: developing new data processing approaches based on Music Information Retrieval (MIR) strategies},
  doi       = {10.25932/publishup-56767},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-567671},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiv, 107},
  year      = {2022},
  abstract  = {Seismology, like many scientific fields, e.g., music information retrieval and speech signal pro- cessing, is experiencing exponential growth in the amount of data acquired by modern seismo- logical networks. In this thesis, I take advantage of the opportunities offered by "big data" and by the methods developed in the areas of music information retrieval and machine learning to predict better the ground motion generated by earthquakes and to study the properties of the surface layers of the Earth. In order to better predict seismic ground motions, I propose two approaches based on unsupervised deep learning methods, an autoencoder network and Generative Adversarial Networks. The autoencoder technique explores a massive amount of ground motion data, evaluates the required parameters, and generates synthetic ground motion data in the Fourier amplitude spectra (FAS) domain. This method is tested on two synthetic datasets and one real dataset. The application on the real dataset shows that the substantial information contained within the FAS data can be encoded to a four to the five-dimensional manifold. Consequently, only a few independent parameters are required for efficient ground motion prediction. I also propose a method based on Conditional Generative Adversarial Networks (CGAN) for simulating ground motion records in the time-frequency and time domains. CGAN generates the time-frequency domains based on the parameters: magnitude, distance, and shear wave velocities to 30 m depth (VS30). After generating the amplitude of the time-frequency domains using the CGAN model, instead of classical conventional methods that assume the amplitude spectra with a random phase spectrum, the phase of the time-frequency domains is recovered by minimizing the observed and reconstructed spectrograms. In the second part of this dissertation, I propose two methods for the monitoring and characterization of near-surface materials and site effect analyses. I implement an autocorrelation function and an interferometry method to monitor the velocity changes of near-surface materials resulting from the Kumamoto earthquake sequence (Japan, 2016). The observed seismic velocity changes during the strong shaking are due to the non-linear response of the near-surface materials. The results show that the velocity changes lasted for about two months after the Kumamoto mainshock. Furthermore, I used the velocity changes to evaluate the in-situ strain-stress relationship. I also propose a method for assessing the site proxy "VS30" using non-invasive analysis. In the proposed method, a dispersion curve of surface waves is inverted to estimate the shear wave velocity of the subsurface. This method is based on the Dix-like linear operators, which relate the shear wave velocity to the phase velocity. The proposed method is fast, efficient, and stable. All of the methods presented in this work can be used for processing "big data" in seismology and for the analysis of weak and strong ground motion data, to predict ground shaking, and to analyze site responses by considering potential time dependencies and nonlinearities.},
  language  = {en}
}
@phdthesis{Schuster2022,
  author    = {Schuster, Valerian},
  title     = {Mechanical and hydraulic properties of Opalinus Clay},
  doi       = {10.25932/publishup-56678},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-566786},
  school      = {Universit{\"a}t Potsdam},
  year      = {2022},
  abstract  = {Deep geological repositories represent a promising solution for the final disposal of nuclear waste. Due to its low permeability, high sorption capacity and self-sealing potential, Opalinus Clay (OPA) is considered a suitable host rock formation for the long-term storage of nuclear waste in Switzerland and Germany. However, the clay formation is characterized by compositional and structural variabilities including the occurrence of carbonate- and quartz-rich layers, pronounced bedding planes as well as tectonic elements such as pre-existing fault zones and fractures, suggesting heterogeneous rock mass properties. Characterizing the heterogeneity of host rock properties is therefore essential for safety predictions of future repositories. This includes a detailed understanding of the mechanical and hydraulic properties, deformation behavior and the underlying deformation processes for an improved assessment of the sealing integrity and long-term safety of a deep repository in OPA. Against this background, this thesis presents the results of deformation experiments performed on intact and artificially fractured specimens of the quartz-rich, sandy and clay-rich, shaly facies of OPA. The experiments focus on the influence of mineralogical composition on the deformation behavior as well as the reactivation and sealing properties of pre-existing faults and fractures at different boundary conditions (e.g., pressure, temperature, strain rate). The anisotropic mechanical properties of the sandy facies of OPA are presented in the first section, which were determined from triaxial deformation experiments using dried and resaturated samples loaded at 0°, 45° and 90° to the bedding plane orientation. A Paterson-type deformation apparatus was used that allowed to investigate how the deformation behavior is influenced by the variation of confining pressure (50 - 100 MPa), temperature (25 - 200 °C), and strain rate (1 × 10-3 - 5 × 10-6 s-1). Constant strain rate experiments revealed brittle to semi-brittle deformation behavior of the sandy facies at the applied conditions. Deformation behavior showed a strong dependence on confining pressure, degree of water saturation as well as bedding orientation, whereas the variation of temperature and strain rate had no significant effect on deformation. Furthermore, the sandy facies displays higher strength and stiffness compared to the clay-rich shaly facies deformed at similar conditions by N{\"u}esch (1991). From the obtained results it can be concluded that cataclastic mechanisms dominate the short-term deformation behavior of dried samples from both facies up to elevated pressure (<200 MPa) and temperature (<200 °C) conditions. The second part presents triaxial deformation tests that were performed to investigate how structural discontinuities affect the deformation behavior of OPA and how the reactivation of preexisting faults is influenced by mineral composition and confining pressure. To this end, dried cylindrical samples of the sandy and shaly facies of OPA were used, which contained a saw-cut fracture oriented at 30° to the long axis. After hydrostatic pre-compaction at 50 MPa, constant strain rate deformation tests were performed at confining pressures of 5, 20 or 35 MPa. With increasing confinement, a gradual transition from brittle, highly localized fault slip including a stress drop at fault reactivation to semi-brittle deformation behavior, characterized by increasing delocalization and non-linear strain hardening without dynamic fault reactivation, can be observed. Brittle localization was limited by the confining pressure at which the fault strength exceeded the matrix yield strength, above which strain partitioning between localized fault slip and distributed matrix deformation occurred. The sandy facies displayed a slightly higher friction coefficient (≈0.48) compared to the shaly facies (≈0.4). In addition, slide-hold-slide tests were conducted, revealing negative or negligible frictional strengthening, which suggests stable creep and long-term weakness of faults in both facies of OPA. The conducted experiments demonstrate that dilatant brittle fault reactivation in OPA may be favored at high overconsolidation ratios and shallow depths, increasing the risk of seismic hazard and the creation of fluid pathways. The final section illustrates how the sealing capacity of fractures in OPA is affected by mineral composition. Triaxial flow-through experiments using Argon-gas were performed with dried samples from the sandy and shaly facies of OPA containing a roughened, artificial fracture. Slate, graywacke, quartzite, natural fault gouge, and granite samples were also tested to highlight the influence of normal stress, mineralogy and diagenesis on the sustainability of fracture transmissivity. With increasing normal stress, a non-linear decrease of fracture transmissivity can be observed that resulted in a permanent reduction of transmissivity after stress release. The transmissivity of rocks with a high portion of strong minerals (e.g., quartz) and high unconfined compressive strength was less sensitive to stress changes. In accordance with this, the sandy facies of OPA displayed a higher initial transmissivity that was less sensitive to stress changes compared to the shaly facies. However, transmissivity of rigid slate was less sensitive to stress changes than the sandy facies of OPA, although the slate is characterized by a higher phyllosilicate content. This demonstrates that in addition to mineral composition, other factors such as the degree of metamorphism, cementation and consolidation have to be considered when evaluating the sealing capacity of phyllosilicate-rich rocks. The results of this thesis highlighted the role of confining pressure on the failure behavior of intact and artificially fractured OPA. Although the quartz-rich sandy facies may be considered as being more favorable for underground constructions due to its higher shear strength and stiffness than the shaly facies, the results indicate that when fractures develop in the sandy facies, they are more conductive and remain more permeable compared to fractures in the clay-dominated shaly facies at a given stress. The results may provide the basis for constitutive models to predict the integrity and evolution of a future repository. Clearly, the influence of composition and consolidation, e.g., by geological burial and uplift, on the mechanical sealing behavior of OPA highlights the need for a detailed site-specific material characterization for a future repository.},
  language  = {en}
}
@phdthesis{Jongejans2022,
  author    = {Jongejans, Loeka Laura},
  title     = {Organic matter stored in ice-rich permafrost},
  doi       = {10.25932/publishup-56491},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-564911},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxiii, 178},
  year      = {2022},
  abstract  = {The Arctic is changing rapidly and permafrost is thawing. Especially ice-rich permafrost, such as the late Pleistocene Yedoma, is vulnerable to rapid and deep thaw processes such as surface subsidence after the melting of ground ice. Due to permafrost thaw, the permafrost carbon pool is becoming increasingly accessible to microbes, leading to increased greenhouse gas emissions, which enhances the climate warming. The assessment of the molecular structure and biodegradability of permafrost organic matter (OM) is highly needed. My research revolves around the question "how does permafrost thaw affect its OM storage?" More specifically, I assessed (1) how molecular biomarkers can be applied to characterize permafrost OM, (2) greenhouse gas production rates from thawing permafrost, and (3) the quality of OM of frozen and (previously) thawed sediments. I studied deep (max. 55 m) Yedoma and thawed Yedoma permafrost sediments from Yakutia (Sakha Republic). I analyzed sediment cores taken below thermokarst lakes on the Bykovsky Peninsula (southeast of the Lena Delta) and in the Yukechi Alas (Central Yakutia), and headwall samples from the permafrost cliff Sobo-Sise (Lena Delta) and the retrogressive thaw slump Batagay (Yana Uplands). I measured biomarker concentrations of all sediment samples. Furthermore, I carried out incubation experiments to quantify greenhouse gas production in thawing permafrost. I showed that the biomarker proxies are useful to assess the source of the OM and to distinguish between OM derived from terrestrial higher plants, aquatic plants and microbial activity. In addition, I showed that some proxies help to assess the degree of degradation of permafrost OM, especially when combined with sedimentological data in a multi-proxy approach. The OM of Yedoma is generally better preserved than that of thawed Yedoma sediments. The greenhouse gas production was highest in the permafrost sediments that thawed for the first time, meaning that the frozen Yedoma sediments contained most labile OM. Furthermore, I showed that the methanogenic communities had established in the recently thawed sediments, but not yet in the still-frozen sediments. My research provided the first molecular biomarker distributions and organic carbon turnover data as well as insights in the state and processes in deep frozen and thawed Yedoma sediments. These findings show the relevance of studying OM in deep permafrost sediments.},
  language  = {en}
}
@phdthesis{Spallanzani2022,
  author    = {Spallanzani, Roberta},
  title     = {Li and B in ascending magmas: an experimental study on their mobility and isotopic fractionation},
  doi       = {10.25932/publishup-56061},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-560619},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiv, 131},
  year      = {2022},
  abstract  = {This research study focuses on the behaviour of Li and B during magmatic ascent, and decompression-driven degassing related to volcanic systems. The main objective of this dissertation is to determine whether it is possible to use the diffusion properties of the two trace elements as a tool to trace magmatic ascent rate. With this objective, diffusion-couple and decompression experiments have been performed in order to study Li and B mobility in intra-melt conditions first, and then in an evolving system during decompression-driven degassing. Synthetic glasses were prepared with rhyolitic composition and an initial water content of 4.2 wt\%, and all the experiments were performed using an internally heated pressure vessel, in order to ensure a precise control on the experimental parameters such as temperature and pressure. Diffusion-couple experiments were performed with a fix pressure 300 MPa. The temperature was varied in the range of 700-1250 °C with durations between 0 seconds and 24 hours. The diffusion-couple results show that Li diffusivity is very fast and starts already at very low temperature. Significant isotopic fractionation occurs due to the faster mobility of 6Li compared to 7Li. Boron diffusion is also accelerated by the presence of water, but the results of the isotopic ratios are unclear, and further investigation would be necessary to well constrain the isotopic fractionation process of boron in hydrous silicate melts. The isotopic ratios results show that boron isotopic fractionation might be affected by the speciation of boron in the silicate melt structure, as 10B and 11B tend to have tetrahedral and trigonal coordination, respectively. Several decompression experiments were performed at 900 °C and 1000 °C, with pressures going from 300 MPa to 71-77 MPa and durations of 30 minutes, two, five and ten hours, in order to trigger water exsolution and the formation of vesicles in the sample. Textural observations and the calculation of the bubble number density confirmed that the bubble size and distribution after decompression is directly proportional to the decompression rate. The overall SIMS results of Li and B show that the two trace elements tend to progressively decrease their concentration with decreasing decompression rates. This is explained because for longer decompression times, the diffusion of Li and B into the bubbles has more time to progress and the melt continuously loses volatiles as the bubbles expand their volumes. For fast decompression, Li and B results show a concentration increase with a δ7Li and δ11B decrease close to the bubble interface, related to the sudden formation of the gas bubble, and the occurrence of a diffusion process in the opposite direction, from the bubble meniscus to the unaltered melt. When the bubble growth becomes dominant and Li and B start to exsolve into the gas phase, the silicate melt close to the bubble gets depleted in Li and B, because of a stronger diffusion of the trace elements into the bubble. Our data are being applied to different models, aiming to combine the dynamics of bubble nucleation and growth with the evolution of trace elements concentration and isotopic ratios. Here, first considerations on these models will be presented, giving concluding remarks on this research study. All in all, the final remarks constitute a good starting point for further investigations. These results are a promising base to continue to study this process, and Li and B can indeed show clear dependences on decompression-related magma ascent rates in volcanic systems.},
  language  = {en}
}
@phdthesis{Tranter2022,
  author    = {Tranter, Morgan Alan},
  title     = {Numerical quantification of barite reservoir scaling and the resulting injectivity loss in geothermal systems},
  doi       = {10.25932/publishup-56113},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-561139},
  school      = {Universit{\"a}t Potsdam},
  pages     = {131},
  year      = {2022},
  abstract  = {Due to the major role of greenhouse gas emissions in global climate change, the development of non-fossil energy technologies is essential. Deep geothermal energy represents such an alternative, which offers promising properties such as a high base load capability and a large untapped potential. The present work addresses barite precipitation within geothermal systems and the associated reduction in rock permeability, which is a major obstacle to maintaining high efficiency. In this context, hydro-geochemical models are essential to quantify and predict the effects of precipitation on the efficiency of a system. The objective of the present work is to quantify the induced injectivity loss using numerical and analytical reactive transport simulations. For the calculations, the fractured-porous reservoirs of the German geothermal regions North German Basin (NGB) and Upper Rhine Graben (URG) are considered. Similar depth-dependent precipitation potentials could be determined for both investigated regions (2.8-20.2 g/m3 fluid). However, the reservoir simulations indicate that the injectivity loss due to barite deposition in the NGB is significant (1.8\%-6.4\% per year) and the longevity of the system is affected as a result; this is especially true for deeper reservoirs (3000 m). In contrast, simulations of URG sites indicate a minor role of barite (< 0.1\%-1.2\% injectivity loss per year). The key differences between the investigated regions are reservoir thicknesses and the presence of fractures in the rock, as well as the ionic strength of the fluids. The URG generally has fractured-porous reservoirs with much higher thicknesses, resulting in a greater distribution of precipitates in the subsurface. Furthermore, ionic strengths are higher in the NGB, which accelerates barite precipitation, causing it to occur more concentrated around the wellbore. The more concentrated the precipitates occur around the wellbore, the higher the injectivity loss. In this work, a workflow was developed within which numerical and analytical models can be used to estimate and quantify the risk of barite precipitation within the reservoir of geothermal systems. A key element is a newly developed analytical scaling score that provides a reliable estimate of induced injectivity loss. The key advantage of the presented approach compared to fully coupled reservoir simulations is its simplicity, which makes it more accessible to plant operators and decision makers. Thus, in particular, the scaling score can find wide application within geothermal energy, e.g., in the search for potential plant sites and the estimation of long-term efficiency.},
  language  = {en}
}
@phdthesis{Schoenfeldt2022,
  author    = {Sch{\"o}nfeldt, Elisabeth},
  title     = {Giant landslides in Patagonia, Argentina},
  pages     = {XXII, 156},
  year      = {2022},
  language  = {en}
}
@phdthesis{Mueller2022,
  author    = {M{\"u}ller, Daniela},
  title     = {Abrupt climate changes and extreme events in two different varved lake sediment records},
  doi       = {10.25932/publishup-55833},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-558331},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVIII, 209},
  year      = {2022},
  abstract  = {Different lake systems might reflect different climate elements of climate changes, while the responses of lake systems are also divers, and are not completely understood so far. Therefore, a comparison of lakes in different climate zones, during the high-amplitude and abrupt climate fluctuations of the Last Glacial to Holocene transition provides an exceptional opportunity to investigate distinct natural lake system responses to different abrupt climate changes. The aim of this doctoral thesis was to reconstruct climatic and environmental fluctuations down to (sub-) annual resolution from two different lake systems during the Last Glacial-Interglacial transition (~17 and 11 ka). Lake Gościąż, situated in the temperate central Poland, developed in the Aller{\o}d after recession of the Last Glacial ice sheets. The Dead Sea is located in the Levant (eastern Mediterranean) within a steep gradient from sub-humid to hyper-arid climate, and formed in the mid-Miocene. Despite their differences in sedimentation processes, both lakes form annual laminations (varves), which are crucial for studies of abrupt climate fluctuations. This doctoral thesis was carried out within the DFG project PALEX-II (Paleohydrology and Extreme Floods from the Dead Sea ICDP Core) that investigates extreme hydro-meteorological events in the ICDP core in relation to climate changes, and ICLEA (Virtual Institute of Integrated Climate and Landscape Evolution Analyses) that intends to better the understanding of climate dynamics and landscape evolutions in north-central Europe since the Last Glacial. Further, it contributes to the Helmholtz Climate Initiative REKLIM (Regional Climate Change and Humans) Research Theme 3 "Extreme events across temporal and spatial scales" that investigates extreme events using climate data, paleo-records and model-based simulations. The three main aims were to (1) establish robust chronologies of the lakes, (2) investigate how major and abrupt climate changes affect the lake systems, and (3) to compare the responses of the two varved lakes to these hemispheric-scale climate changes. Robust chronologies are a prerequisite for high-resolved climate and environmental reconstructions, as well as for archive comparisons. Thus, addressing the first aim, the novel chronology of Lake Gościąż was established by microscopic varve counting and Bayesian age-depth modelling in Bacon for a non-varved section, and was corroborated by independent age constrains from 137Cs activity concentration measurements, AMS radiocarbon dating and pollen analysis. The varve chronology reaches from the late Aller{\o}d until AD 2015, revealing more Holocene varves than a previous study of Lake Gościąż suggested. Varve formation throughout the complete Younger Dryas (YD) even allowed the identification of annually- to decadal-resolved leads and lags in proxy responses at the YD transitions. The lateglacial chronology of the Dead Sea (DS) was thus far mainly based on radiocarbon and U/Th-dating. In the unique ICDP core from the deep lake centre, continuous search for cryptotephra has been carried out in lateglacial sediments between two prominent gypsum deposits - the Upper and Additional Gypsum Units (UGU and AGU, respectively). Two cryptotephras were identified with glass analyses that correlate with tephra deposits from the S{\"u}phan and Nemrut volcanoes indicating that the AGU is ~1000 years younger than previously assumed, shifting it into the YD, and the underlying varved interval into the B{\o}lling/Aller{\o}d, contradicting previous assumptions. Using microfacies analyses, stable isotopes and temperature reconstructions, the second aim was achieved at Lake Gościąż. The YD lake system was dynamic, characterized by higher aquatic bioproductivity, more re-suspended material and less anoxia than during the Aller{\o}d and Early Holocene, mainly influenced by stronger water circulation and catchment erosion due to stronger westerly winds and less lake sheltering. Cooling at the YD onset was ~100 years longer than the final warming, while environmental proxies lagged the onset of cooling by ~90 years, but occurred contemporaneously during the termination of the YD. Chironomid-based temperature reconstructions support recent studies indicating mild YD summer temperatures. Such a comparison of annually-resolved proxy responses to both abrupt YD transitions is rare, because most European lake archives do not preserve varves during the YD. To accomplish the second aim at the DS, microfacies analyses were performed between the UGU (~17 ka) and Holocene onset (~11 ka) in shallow- (Masada) and deep-water (ICDP core) environments. This time interval is marked by a huge but fluctuating lake level drop and therefore the complete transition into the Holocene is only recorded in the deep-basin ICDP core. In this thesis, this transition was investigated for the first time continuously and in detail. The final two pronounced lake level drops recorded by deposition of the UGU and AGU, were interrupted by one millennium of relative depositional stability and a positive water budget as recorded by aragonite varve deposition interrupted by only a few event layers. Further, intercalation of aragonite varves between the gypsum beds of the UGU and AGU shows that these generally dry intervals were also marked by decadal- to centennial-long rises in lake level. While continuous aragonite varves indicate decadal-long stable phases, the occurrence of thicker and more frequent event layers suggests general more instability during the gypsum units. These results suggest a pattern of complex and variable hydroclimate at different time scales during the Lateglacial at the DS. The third aim was accomplished based on the individual studies above that jointly provide an integrated picture of different lake responses to different climate elements of hemispheric-scale abrupt climate changes during the Last Glacial-Interglacial transition. In general, climatically-driven facies changes are more dramatic in the DS than at Lake Gościąż. Further, Lake Gościąż is characterized by continuous varve formation nearly throughout the complete profile, whereas the DS record is widely characterized by extreme event layers, hampering the establishment of a continuous varve chronology. The lateglacial sedimentation in Lake Gościąż is mainly influenced by westerly winds and minor by changes in catchment vegetation, whereas the DS is primarily influenced by changes in winter precipitation, which are caused by temperature variations in the Mediterranean. Interestingly, sedimentation in both archives is more stable during the B{\o}lling/Aller{\o}d and more dynamic during the YD, even when sedimentation processes are different. In summary, this doctoral thesis presents seasonally-resolved records from two lake archives during the Lateglacial (ca 17-11 ka) to investigate the impact of abrupt climate changes in different lake systems. New age constrains from the identification of volcanic glass shards in the lateglacial sediments of the DS allowed the first lithology-based interpretation of the YD in the DS record and its comparison to Lake Gościąż. This highlights the importance of the construction of a robust chronology, and provides a first step for synchronization of the DS with other eastern Mediterranean archives. Further, climate reconstructions from the lake sediments showed variability on different time scales in the different archives, i.e. decadal- to millennial fluctuations in the lateglacial DS, and even annual variations and sub-decadal leads and lags in proxy responses during the rapid YD transitions in Lake Gościąż. This showed the importance of a comparison of different lake archives to better understand the regional and local impacts of hemispheric-scale climate variability. An unprecedented example is demonstrated here of how different lake systems show different lake responses and also react to different climate elements of abrupt climate changes. This further highlights the importance of the understanding of the respective lake system for climate reconstructions.},
  language  = {en}
}
@phdthesis{Pan2022,
  author    = {Pan, Mengdi},
  title     = {Systematic studies on the thermodynamic properties of gas hydrates and their formation/dissociation/transformation behaviors},
  doi       = {10.25932/publishup-55476},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-554760},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XX, 192},
  year      = {2022},
  abstract  = {Gas hydrates are ice-like crystalline compounds made of water cavities that retain various types of guest molecules. Natural gas hydrates are CH4-rich but also contain higher hydrocarbons as well as CO2, H2S, etc. They are highly dependent of local pressure and temperature conditions. Considering the high energy content, natural gas hydrates are artificially dissociated for the production of methane gas. Besides, they may also dissociate in response to global warming. It is therefore crucial to investigate the hydrate nucleation and growth process at a molecular level. The understanding of how guest molecules in the hydrate cavities respond to warming climate or gas injection is also of great importance. This thesis is concerned with a systematic investigation of simple and mixed gas hydrates at conditions relevant to the natural hydrate reservoir in Qilian Mountain permafrost, China. A high-pressure cell that integrated into the confocal Raman spectroscopy ensured a precise and continuous characterization of the hydrate phase during formation/dissociation/transformation processes with a high special and spectral resolution. By applying laboratory experiments, the formation of mixed gas hydrates containing other hydrocarbons besides methane was simulated in consideration of the effects from gas supply conditions and sediments. The results revealed a preferential enclathration of different guest molecules in hydrate cavities and further refute the common hypothesis of the coexistence of hydrate phases due to a changing feed gas phase. However, the presence of specific minerals and organic compounds in sediments may have significant impacts on the coexisting solid phases. With regard to the dissociation, the formation damage caused by fines mobilization and migration during hydrate decomposition was reported for the first time, illustrating the complex interactions between fine grains and hydrate particles. Gas hydrates, starting from simple CH4 hydrates to binary CH4—C3H8 hydrates and multi-component mixed hydrates were decomposed by thermal stimulation mimicking global warming. The mechanisms of guest substitution in hydrate structures were studied through the experimental data obtained from CH4—CO2, CH4—mixed gas hydrates and mixed gas hydrates—CO2 systems. For the first time, a second transformation behavior was documented during the transformation process from CH4 hydrates to CO2-rich mixed hydrates. Most of the crystals grew or maintained when exposed to CO2 gas while some others decreased in sizes and even disappeared over time. The highlight of the two last experimental simulations was to visualize and characterize the hydrate crystals which were at different structural transition stages. These experimental simulations enhanced our knowledge about the mixed gas hydrates in natural reservoirs and improved our capability to assess the response to global warming.},
  language  = {en}
}
@phdthesis{Brill2022,
  author    = {Brill, Fabio Alexander},
  title     = {Applications of machine learning and open geospatial data in flood risk modelling},
  doi       = {10.25932/publishup-55594},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-555943},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xix, 124},
  year      = {2022},
  abstract  = {Der technologische Fortschritt erlaubt es, zunehmend komplexe Vorhersagemodelle auf Basis immer gr{\"o}ßerer Datens{\"a}tze zu produzieren. F{\"u}r das Risikomanagement von Naturgefahren sind eine Vielzahl von Modellen als Entscheidungsgrundlage notwendig, z.B. in der Auswertung von Beobachtungsdaten, f{\"u}r die Vorhersage von Gefahrenszenarien, oder zur statistischen Absch{\"a}tzung der zu erwartenden Sch{\"a}den. Es stellt sich also die Frage, inwiefern moderne Modellierungsans{\"a}tze wie das maschinelle Lernen oder Data-Mining in diesem Themenbereich sinnvoll eingesetzt werden k{\"o}nnen. Zus{\"a}tzlich ist im Hinblick auf die Datenverf{\"u}gbarkeit und -zug{\"a}nglichkeit ein Trend zur {\"O}ffnung (open data) zu beobachten. Thema dieser Arbeit ist daher, die M{\"o}glichkeiten und Grenzen des maschinellen Lernens und frei verf{\"u}gbarer Geodaten auf dem Gebiet der Hochwasserrisikomodellierung im weiteren Sinne zu untersuchen. Da dieses {\"u}bergeordnete Thema sehr breit ist, werden einzelne relevante Aspekte herausgearbeitet und detailliert betrachtet. Eine prominente Datenquelle im Bereich Hochwasser ist die satellitenbasierte Kartierung von {\"U}berflutungsfl{\"a}chen, die z.B. {\"u}ber den Copernicus Service der Europ{\"a}ischen Union frei zur Verf{\"u}gung gestellt werden. Große Hoffnungen werden in der wissenschaftlichen Literatur in diese Produkte gesetzt, sowohl f{\"u}r die akute Unterst{\"u}tzung der Einsatzkr{\"a}fte im Katastrophenfall, als auch in der Modellierung mittels hydrodynamischer Modelle oder zur Schadensabsch{\"a}tzung. Daher wurde ein Fokus in dieser Arbeit auf die Untersuchung dieser Flutmasken gelegt. Aus der Beobachtung, dass die Qualit{\"a}t dieser Produkte in bewaldeten und urbanen Gebieten unzureichend ist, wurde ein Verfahren zur nachtr{\"a}glichenVerbesserung mittels maschinellem Lernen entwickelt. Das Verfahren basiert auf einem Klassifikationsalgorithmus der nur Trainingsdaten von einer vorherzusagenden Klasse ben{\"o}tigt, im konkreten Fall also Daten von {\"U}berflutungsfl{\"a}chen, nicht jedoch von der negativen Klasse (trockene Gebiete). Die Anwendung f{\"u}r Hurricane Harvey in Houston zeigt großes Potenzial der Methode, abh{\"a}ngig von der Qualit{\"a}t der urspr{\"u}nglichen Flutmaske. Anschließend wird anhand einer prozessbasierten Modellkette untersucht, welchen Einfluss implementierte physikalische Prozessdetails auf das vorhergesagte statistische Risiko haben. Es wird anschaulich gezeigt, was eine Risikostudie basierend auf etablierten Modellen leisten kann. Solche Modellketten sind allerdings bereits f{\"u}r Flusshochwasser sehr komplex, und f{\"u}r zusammengesetzte oder kaskadierende Ereignisse mit Starkregen, Sturzfluten, und weiteren Prozessen, kaum vorhanden. Im vierten Kapitel dieser Arbeit wird daher getestet, ob maschinelles Lernen auf Basis von vollst{\"a}ndigen Schadensdaten einen direkteren Weg zur Schadensmodellierung erm{\"o}glicht, der die explizite Konzeption einer solchen Modellkette umgeht. Dazu wird ein staatlich erhobener Datensatz der gesch{\"a}digten Geb{\"a}ude w{\"a}hrend des schweren El Ni{\~n}o Ereignisses 2017 in Peru verwendet. In diesem Kontext werden auch die M{\"o}glichkeiten des Data-Mining zur Extraktion von Prozessverst{\"a}ndnis ausgelotet. Es kann gezeigt werden, dass diverse frei verf{\"u}gbare Geodaten n{\"u}tzliche Informationen f{\"u}r die Gefahren- und Schadensmodellierung von komplexen Flutereignissen liefern, z.B. satellitenbasierte Regenmessungen, topographische und hydrographische Information, kartierte Siedlungsfl{\"a}chen, sowie Indikatoren aus Spektraldaten. Zudem zeigen sich Erkenntnisse zu den Sch{\"a}digungsprozessen, die im Wesentlichen mit den vorherigen Erwartungen in Einklang stehen. Die maximale Regenintensit{\"a}t wirkt beispielsweise in St{\"a}dten und steilen Schluchten st{\"a}rker sch{\"a}digend, w{\"a}hrend die Niederschlagssumme in tiefliegenden Flussgebieten und bewaldeten Regionen als aussagekr{\"a}ftiger befunden wurde. L{\"a}ndliche Gebiete in Peru weisen in der pr{\"a}sentierten Studie eine h{\"o}here Vulnerabilit{\"a}t als die Stadtgebiete auf. Jedoch werden auch die grunds{\"a}tzlichen Grenzen der Methodik und die Abh{\"a}ngigkeit von spezifischen Datens{\"a}tzen and Algorithmen offenkundig. In der {\"u}bergreifenden Diskussion werden schließlich die verschiedenen Methoden - prozessbasierte Modellierung, pr{\"a}diktives maschinelles Lernen, und Data-Mining - mit Blick auf die Gesamtfragestellungen evaluiert. Im Bereich der Gefahrenbeobachtung scheint eine Fokussierung auf neue Algorithmen sinnvoll. Im Bereich der Gefahrenmodellierung, insbesondere f{\"u}r Flusshochwasser, wird eher die Verbesserung von physikalischen Modellen, oder die Integration von prozessbasierten und statistischen Verfahren angeraten. In der Schadensmodellierung fehlen nach wie vor die großen repr{\"a}sentativen Datens{\"a}tze, die f{\"u}r eine breite Anwendung von maschinellem Lernen Voraussetzung ist. Daher ist die Verbesserung der Datengrundlage im Bereich der Sch{\"a}den derzeit als wichtiger einzustufen als die Auswahl der Algorithmen.},
  language  = {en}
}
@phdthesis{Niemz2022,
  author    = {Niemz, Peter},
  title     = {Imaging and modeling of hydraulic fractures in crystalline rock via induced seismic activity},
  doi       = {10.25932/publishup-55659},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-556593},
  school      = {Universit{\"a}t Potsdam},
  pages     = {135},
  year      = {2022},
  abstract  = {Enhanced geothermal systems (EGS) are considered a cornerstone of future sustainable energy production. In such systems, high-pressure fluid injections break the rock to provide pathways for water to circulate in and heat up. This approach inherently induces small seismic events that, in rare cases, are felt or can even cause damage. Controlling and reducing the seismic impact of EGS is crucial for a broader public acceptance. To evaluate the applicability of hydraulic fracturing (HF) in EGS and to improve the understanding of fracturing processes and the hydromechanical relation to induced seismicity, six in-situ, meter-scale HF experiments with different injection schemes were performed under controlled conditions in crystalline rock in a depth of 410 m at the {\"A}sp{\"o} Hard Rock Laboratory (Sweden). I developed a semi-automated, full-waveform-based detection, classification, and location workflow to extract and characterize the acoustic emission (AE) activity from the continuous recordings of 11 piezoelectric AE sensors. Based on the resulting catalog of 20,000 AEs, with rupture sizes of cm to dm, I mapped and characterized the fracture growth in great detail. The injection using a novel cyclic injection scheme (HF3) had a lower seismic impact than the conventional injections. HF3 induced fewer AEs with a reduced maximum magnitude and significantly larger b-values, implying a decreased number of large events relative to the number of small ones. Furthermore, HF3 showed an increased fracture complexity with multiple fractures or a fracture network. In contrast, the conventional injections developed single, planar fracture zones (Publication 1). An independent, complementary approach based on a comparison of modeled and observed tilt exploits transient long-period signals recorded at the horizontal components of two broad-band seismometers a few tens of meters apart from the injections. It validated the efficient creation of hydraulic fractures and verified the AE-based fracture geometries. The innovative joint analysis of AEs and tilt signals revealed different phases of the fracturing process, including the (re-)opening, growth, and aftergrowth of fractures, and provided evidence for the reactivation of a preexisting fault in one of the experiments (Publication 2). A newly developed network-based waveform-similarity analysis applied to the massive AE activity supports the latter finding. To validate whether the reduction of the seismic impact as observed for the cyclic injection schemes during the {\"A}sp{\"o} mine-scale experiments is transferable to other scales, I additionally calculated energy budgets for injection experiments from previously conducted laboratory tests and from a field application. Across all three scales, the cyclic injections reduce the seismic impact, as depicted by smaller maximum magnitudes, larger b-values, and decreased injection efficiencies (Publication 3).},
  language  = {en}
}
@phdthesis{Richter2022,
  author    = {Richter, Maximilian Jacob Enzo Amandus},
  title     = {Continental rift dynamics across the scales},
  doi       = {10.25932/publishup-55060},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-550606},
  school      = {Universit{\"a}t Potsdam},
  pages     = {129},
  year      = {2022},
  abstract  = {Localisation of deformation is a ubiquitous feature in continental rift dynamics and observed across drastically different time and length scales. This thesis comprises one experimental and two numerical modelling studies investigating strain localisation in (1) a ductile shear zone induced by a material heterogeneity and (2) in an active continental rift setting. The studies are related by the fact that the weakening mechanisms on the crystallographic and grain size scale enable bulk rock weakening, which fundamentally enables the formation of shear zones, continental rifts and hence plate tectonics. Aiming to investigate the controlling mechanisms on initiation and evolution of a shear zone, the torsion experiments of the experimental study were conducted in a Patterson type apparatus with strong Carrara marble cylinders with a weak, planar Solnhofen limestone inclusion. Using state-of-the-art numerical modelling software, the torsion experiments were simulated to answer questions regarding localisation procedure like stress distribution or the impact of rheological weakening. 2D numerical models were also employed to integrate geophysical and geological data to explain characteristic tectonic evolution of the Southern and Central Kenya Rift. Key elements of the numerical tools are a randomized initial strain distribution and the usage of strain softening. During the torsion experiments, deformation begins to localise at the limestone inclusion tips in a process zone, which propagates into the marble matrix with increasing deformation until a ductile shear zone is established. Minor indicators for coexisting brittle deformation are found close to the inclusion tip and presumed to slightly facilitate strain localisation besides the dominant ductile deformation processes. The 2D numerical model of the torsion experiment successfully predicts local stress concentration and strain rate amplification ahead of the inclusion in first order agreement with the experimental results. A simple linear parametrization of strain weaking enables high accuracy reproduction of phenomenological aspects of the observed weakening. The torsion experiments suggest that loading conditions do not affect strain localisation during high temperature deformation of multiphase material with high viscosity contrasts. A numerical simulation can provide a way of analysing the process zone evolution virtually and extend the examinable frame. Furthermore, the nested structure and anastomosing shape of an ultramylonite band was mimicked with an additional second softening step. Rheological weakening is necessary to establish a shear zone in a strong matrix around a weak inclusion and for ultramylonite formation. Such strain weakening laws are also incorporated into the numerical models of the Southern and Central Kenya Rift that capture the characteristic tectonic evolution. A three-stage early rift evolution is suggested that starts with (1) the accommodation of strain by a single border fault and flexure of the hanging-wall crust, after which (2) faulting in the hanging-wall and the basin centre increases before (3) the early-stage asymmetry is lost and basinward localisation of deformation occurs. Along-strike variability of rifts can be produced by modifying the initial random noise distribution. In summary, the three studies address selected aspects of the broad range of mechanisms and processes that fundamentally enable the deformation of rock and govern the localisation patterns across the scales. In addition to the aforementioned results, the first and second manuscripts combined, demonstrate a procedure to find new or improve on existing numerical formulations for specific rheologies and their dynamic weakening. These formulations are essential in addressing rock deformation from the grain to the global scale. As within the third study of this thesis, where geodynamic controls on the evolution of a rift were examined and acquired by the integration of geological and geophysical data into a numerical model.},
  language  = {en}
}
@phdthesis{Hennig2022,
  author    = {Hennig, Theresa},
  title     = {Uranium migration in the Opalinus Clay quantified on the host rock scale with reactive transport simulations},
  doi       = {10.25932/publishup-55270},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-552700},
  school      = {Universit{\"a}t Potsdam},
  pages     = {161},
  year      = {2022},
  abstract  = {Humankind and their environment need to be protected from the harmful effects of spent nuclear fuel, and therefore disposal in deep geological formations is favoured worldwide. Suitability of potential host rocks is evaluated, among others, by the retention capacity with respect to radionuclides. Safety assessments are based on the quantification of radionuclide migration lengths with numerical simulations as experiments cannot cover the required temporal (1 Ma) and spatial scales (>100 m). Aim of the present thesis is to assess the migration of uranium, a geochemically complex radionuclide, in the potential host rock Opalinus Clay. Radionuclide migration in clay formations is governed by diffusion due to their low permeability and retarded by sorption. Both processes highly depend on pore water geochemistry and mineralogy that vary between different facies. Diffusion is quantified with the single-component (SC) approach using one diffusion coefficient for all species and the process-based multi-component (MC) option. With this, each species is assigned its own diffusion coefficient and the interaction with the diffuse double layer is taken into account. Sorption is integrated via a bottom-up approach using mechanistic surface complexation models and cation exchange. Therefore, reactive transport simulations are conducted with the geochemical code PHREEQC to quantify uranium migration, i.e. diffusion and sorption, as a function of mineralogical and geochemical heterogeneities on the host rock scale. Sorption processes are facies dependent. Migration lengths vary between the Opalinus Clay facies by up to 10 m. Thereby, the geochemistry of the pore water, in particular the partial pressure of carbon dioxide (pCO2), is more decisive for the sorption capacity than the amount of clay minerals. Nevertheless, higher clay mineral quantities compensate geochemical variations. Consequently, sorption processes must be quantified as a function of pore water geochemistry in contact with the mineral assemblage. Uranium diffusion in the Opalinus Clay is facies independent. Speciation is dominated by aqueous ternary complexes of U(VI) with calcium and carbonate. Differences in the migration lengths between SC and MC diffusion are with +/-5 m negligible. Further, the application of the MC approach highly depends on the quality and availability of the underlying data. Therefore, diffusion processes can be adequately quantified with the SC approach using experimentally determined diffusion coefficients. The hydrogeological system governs pore water geochemistry within the formation rather than the mineralogy. Diffusive exchange with the adjacent aquifers established geochemical gradients over geological time scales that can enhance migration by up to 25 m. Consequently, uranium sorption processes must be quantified following the identified priority: pCO2 > hydrogeology > mineralogy. The presented research provides a workflow and orientation for other potential disposal sites with similar pore water geochemistry due to the identified mechanisms and dependencies. With a maximum migration length of 70 m, the retention capacity of the Opalinus Clay with respect to uranium is sufficient to fulfill the German legal minimum requirement of a thickness of at least 100 m.},
  language  = {en}
}
@phdthesis{Farkas2022,
  author    = {Farkas, Marton Pal},
  title     = {Hydraulic fracturing in hard rock - numerical studies from laboratory to reservoir scale},
  doi       = {10.25932/publishup-54934},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549343},
  school      = {Universit{\"a}t Potsdam},
  pages     = {155},
  year      = {2022},
  abstract  = {Hydraulic-driven fractures play a key role in subsurface energy technologies across several scales. By injecting fluid at high hydraulic pressure into rock with intrinsic low permeability, in-situ stress field and fracture development pattern can be characterised as well as rock permeability can be enhanced. Hydraulic fracturing is a commercial standard procedure for enhanced oil and gas production of rock reservoirs with low permeability in petroleum industry. However, in EGS utilization, a major geological concern is the unsolicited generation of earthquakes due to fault reactivation, referred to as induced seismicity, with a magnitude large enough to be felt on the surface or to damage facilities and buildings. Furthermore, reliable interpretation of hydraulic fracturing tests for stress measurement is a great challenge for the energy technologies. Therefore, in this cumulative doctoral thesis the following research questions are investigated. (1): How do hydraulic fractures grow in hard rock at various scales?; (2): Which parameters control hydraulic fracturing and hydro-mechanical coupling?; and (3): How can hydraulic fracturing in hard rock be modelled? In the laboratory scale study, several laboratory hydraulic fracturing experiments are investigated numerically using Irazu2D that were performed on intact cubic Pocheon granite samples from South Korea applying different injection protocols. The goal of the laboratory experiments is to test the concept of cyclic soft stimulation which may enable sustainable permeability enhancement (Publication 1). In the borehole scale study, hydraulic fracturing tests are reported that were performed in boreholes located in central Hungary to determine the in-situ stress for a geological site investigation. At depth of about 540 m, the recorded pressure versus time curves in mica schist with low dip angle foliation show atypical evolution. In order to provide explanation for this observation, a series of discrete element computations using Particle Flow Code 2D are performed (Publication 2). In the reservoir scale study, the hydro-mechanical behaviour of fractured crystalline rock due to one of the five hydraulic stimulations at the Pohang Enhanced Geothermal site in South Korea is studied. Fluid pressure perturbation at faults of several hundred-meter lengths during hydraulic stimulation is simulated using FracMan (Publication 3). The doctoral research shows that the resulting hydraulic fracturing geometry will depend "locally", i.e. at the length scale of representative elementary volume (REV) and below that (sub-REV), on the geometry and strength of natural fractures, and "globally", i.e. at super-REV domain volume, on far-field stresses. Regarding hydro-mechanical coupling, it is suggested to define separate coupling relationship for intact rock mass and natural fractures. Furthermore, the relative importance of parameters affecting the magnitude of formation breakdown pressure, a parameter characterising hydro-mechanical coupling, is defined. It can be also concluded that there is a clear gap between the capacity of the simulation software and the complexity of the studied problems. Therefore, the computational time of the simulation of complex hydraulic fracture geometries must be reduced while maintaining high fidelity simulation results. This can be achieved either by extending the computational resources via parallelization techniques or using time scaling techniques. The ongoing development of used numerical models focuses on tackling these methodological challenges.},
  language  = {en}
}
@phdthesis{Forster2021,
  author    = {Forster, Florian},
  title     = {Continuous microgravity monitoring of the Þeistareykir geothermal field (North Iceland)},
  doi       = {10.25932/publishup-54851},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-548517},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVII, 164},
  year      = {2021},
  abstract  = {In my doctoral thesis, I examine continuous gravity measurements for monitoring of the geothermal site at Þeistareykir in North Iceland. With the help of high-precision superconducting gravity meters (iGravs), I investigate underground mass changes that are caused by operation of the geothermal power plant (i.e. by extraction of hot water and reinjection of cold water). The overall goal of this research project is to make a statement about the sustainable use of the geothermal reservoir, from which also the Icelandic energy supplier and power plant operator Landsvirkjun should benefit. As a first step, for investigating the performance and measurement stability of the gravity meters, in summer 2017, I performed comparative measurements at the gravimetric observatory J9 in Strasbourg. From the three-month gravity time series, I examined calibration, noise and drift behaviour of the iGravs in comparison to stable long-term time series of the observatory superconducting gravity meters. After preparatory work in Iceland (setup of gravity stations, additional measuring equipment and infrastructure, discussions with Landsvirkjun and meetings with the Icelandic partner institute ISOR), gravity monitoring at Þeistareykir was started in December 2017. With the help of the iGrav records of the initial 18 months after start of measurements, I carried out the same investigations (on calibration, noise and drift behaviour) as in J9 to understand how the transport of the superconducting gravity meters to Iceland may influence instrumental parameters. In the further course of this work, I focus on modelling and reduction of local gravity contributions at Þeistareykir. These comprise additional mass changes due to rain, snowfall and vertical surface displacements that superimpose onto the geothermal signal of the gravity measurements. For this purpose, I used data sets from additional monitoring sensors that are installed at each gravity station and adapted scripts for hydro-gravitational modelling. The third part of my thesis targets geothermal signals in the gravity measurements. Together with my PhD colleague Nolwenn Portier from France, I carried out additional gravity measurements with a Scintrex CG5 gravity meter at 26 measuring points within the geothermal field in the summers of 2017, 2018 and 2019. These annual time-lapse gravity measurements are intended to increase the spatial coverage of gravity data from the three continuous monitoring stations to the entire geothermal field. The combination of CG5 and iGrav observations, as well as annual reference measurements with an FG5 absolute gravity meter represent the hybrid gravimetric monitoring method for Þeistareykir. Comparison of the gravimetric data to local borehole measurements (of groundwater levels, geothermal extraction and injection rates) is used to relate the observed gravity changes to the actually extracted (and reinjected) geothermal fluids. An approach to explain the observed gravity signals by means of forward modelling of the geothermal production rate is presented at the end of the third (hybrid gravimetric) study. Further modelling with the help of the processed gravity data is planned by Landsvirkjun. In addition, the experience from time-lapse and continuous gravity monitoring will be used for future gravity measurements at the Krafla geothermal field 22 km south-east of Þeistareykir.},
  language  = {en}
}
@phdthesis{Neuharth2022,
  author    = {Neuharth, Derek},
  title     = {Evolution of divergent and strike-slip boundaries in response to surface processes},
  doi       = {10.25932/publishup-54940},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549403},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 108},
  year      = {2022},
  abstract  = {Plate tectonics describes the movement of rigid plates at the surface of the Earth as well as their complex deformation at three types of plate boundaries: 1) divergent boundaries such as rift zones and mid-ocean ridges, 2) strike-slip boundaries where plates grind past each other, such as the San Andreas Fault, and 3) convergent boundaries that form large mountain ranges like the Andes. The generally narrow deformation zones that bound the plates exhibit complex strain patterns that evolve through time. During this evolution, plate boundary deformation is driven by tectonic forces arising from Earth's deep interior and from within the lithosphere, but also by surface processes, which erode topographic highs and deposit the resulting sediment into regions of low elevation. Through the combination of these factors, the surface of the Earth evolves in a highly dynamic way with several feedback mechanisms. At divergent boundaries, for example, tensional stresses thin the lithosphere, forcing uplift and subsequent erosion of rift flanks, which creates a sediment source. Meanwhile, the rift center subsides and becomes a topographic low where sediments accumulate. This mass transfer from foot- to hanging wall plays an important role during rifting, as it prolongs the activity of individual normal faults. When rifting continues, continents are eventually split apart, exhuming Earth's mantle and creating new oceanic crust. Because of the complex interplay between deep tectonic forces that shape plate boundaries and mass redistribution at the Earth's surface, it is vital to understand feedbacks between the two domains and how they shape our planet. In this study I aim to provide insight on two primary questions: 1) How do divergent and strike-slip plate boundaries evolve? 2) How is this evolution, on a large temporal scale and a smaller structural scale, affected by the alteration of the surface through erosion and deposition? This is done in three chapters that examine the evolution of divergent and strike-slip plate boundaries using numerical models. Chapter 2 takes a detailed look at the evolution of rift systems using two-dimensional models. Specifically, I extract faults from a range of rift models and correlate them through time to examine how fault networks evolve in space and time. By implementing a two-way coupling between the geodynamic code ASPECT and landscape evolution code FastScape, I investigate how the fault network and rift evolution are influenced by the system's erosional efficiency, which represents many factors like lithology or climate. In Chapter 3, I examine rift evolution from a three-dimensional perspective. In this chapter I study linkage modes for offset rifts to determine when fast-rotating plate-boundary structures known as continental microplates form. Chapter 4 uses the two-way numerical coupling between tectonics and landscape evolution to investigate how a strike-slip boundary responds to large sediment loads, and whether this is sufficient to form an entirely new type of flexural strike-slip basin.},
  language  = {en}
}
@phdthesis{RodriguezPiceda2022,
  author    = {Rodriguez Piceda, Constanza},
  title     = {Thermomechanical state of the southern Central Andes},
  doi       = {10.25932/publishup-54927},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549275},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 228},
  year      = {2022},
  abstract  = {The Andes are a ~7000 km long N-S trending mountain range developed along the South American western continental margin. Driven by the subduction of the oceanic Nazca plate beneath the continental South American plate, the formation of the northern and central parts of the orogen is a type case for a non-collisional orogeny. In the southern Central Andes (SCA, 29°S-39°S), the oceanic plate changes the subduction angle between 33°S and 35°S from almost horizontal (< 5° dip) in the north to a steeper angle (~30° dip) in the south. This sector of the Andes also displays remarkable along- and across- strike variations of the tectonic deformation patterns. These include a systematic decrease of topographic elevation, of crustal shortening and foreland and orogenic width, as well as an alternation of the foreland deformation style between thick-skinned and thin-skinned recorded along- and across the strike of the subduction zone. Moreover, the SCA are a very seismically active region. The continental plate is characterized by a relatively shallow seismicity (< 30 km depth) which is mainly focussed at the transition from the orogen to the lowland areas of the foreland and the forearc; in contrast, deeper seismicity occurs below the interiors of the northern foreland. Additionally, frequent seismicity is also recorded in the shallow parts of the oceanic plate and in a sector of the flat slab segment between 31°S and 33°S. The observed spatial heterogeneity in tectonic and seismic deformation in the SCA has been attributed to multiple causes, including variations in sediment thickness, the presence of inherited structures and changes in the subduction angle of the oceanic slab. However, there is no study that inquired the relationship between the long-term rheological configuration of the SCA and the spatial deformation patterns. Moreover, the effects of the density and thickness configuration of the continental plate and of variations in the slab dip angle in the rheological state of the lithosphere have been not thoroughly investigated yet. Since rheology depends on composition, pressure and temperature, a detailed characterization of the compositional, structural and thermal fields of the lithosphere is needed. Therefore, by using multiple geophysical approaches and data sources, I constructed the following 3D models of the SCA lithosphere: (i) a seismically-constrained structural and density model that was tested against the gravity field; (ii) a thermal model integrating the conversion of mantle shear-wave velocities to temperature with steady-state conductive calculations in the uppermost lithosphere (< 50 km depth), validated by temperature and heat-flow measurements; and (iii) a rheological model of the long-term lithospheric strength using as input the previously-generated models. The results of this dissertation indicate that the present-day thermal and rheological fields of the SCA are controlled by different mechanisms at different depths. At shallow depths (< 50 km), the thermomechanical field is modulated by the heterogeneous composition of the continental lithosphere. The overprint of the oceanic slab is detectable where the oceanic plate is shallow (< 85 km depth) and the radiogenic crust is thin, resulting in overall lower temperatures and higher strength compared to regions where the slab is steep and the radiogenic crust is thick. At depths > 50 km, largest temperatures variations occur where the descending slab is detected, which implies that the deep thermal field is mainly affected by the slab dip geometry. The outcomes of this thesis suggests that long-term thermomechanical state of the lithosphere influences the spatial distribution of seismic deformation. Most of the seismicity within the continental plate occurs above the modelled transition from brittle to ductile conditions. Additionally, there is a spatial correlation between the location of these events and the transition from the mechanically strong domains of the forearc and foreland to the weak domain of the orogen. In contrast, seismicity within the oceanic plate is also detected where long-term ductile conditions are expected. I therefore analysed the possible influence of additional mechanisms triggering these earthquakes, including the compaction of sediments in the subduction interface and dehydration reactions in the slab. To that aim, I carried out a qualitative analysis of the state of hydration in the mantle using the ratio between compressional- and shear-wave velocity (vp/vs ratio) from a previous seismic tomography. The results from this analysis indicate that the majority of the seismicity spatially correlates with hydrated areas of the slab and overlying continental mantle, with the exception of the cluster within the flat slab segment. In this region, earthquakes are likely triggered by flexural processes where the slab changes from a flat to a steep subduction angle. First-order variations in the observed tectonic patterns also seem to be influenced by the thermomechanical configuration of the lithosphere. The mechanically strong domains of the forearc and foreland, due to their resistance to deformation, display smaller amounts of shortening than the relatively weak orogenic domain. In addition, the structural and thermomechanical characteristics modelled in this dissertation confirm previous analyses from geodynamic models pointing to the control of the observed heterogeneities in the orogen and foreland deformation style. These characteristics include the lithospheric and crustal thickness, the presence of weak sediments and the variations in gravitational potential energy. Specific conditions occur in the cold and strong northern foreland, which is characterized by active seismicity and thick-skinned structures, although the modelled crustal strength exceeds the typical values of externally-applied tectonic stresses. The additional mechanisms that could explain the strain localization in a region that should resist deformation are: (i) increased tectonic forces coming from the steepening of the slab and (ii) enhanced weakening along inherited structures from pre-Andean deformation events. Finally, the thermomechanical conditions of this sector of the foreland could be a key factor influencing the preservation of the flat subduction angle at these latitudes of the SCA.},
  language  = {en}
}
@phdthesis{Steding2022,
  author    = {Steding, Svenja},
  title     = {Geochemical and Hydraulic Modeling of Cavernous Structures in Potash Seams},
  doi       = {10.25932/publishup-54818},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-548182},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IX, 104},
  year      = {2022},
  abstract  = {Salt deposits offer a variety of usage types. These include the mining of rock salt and potash salt as important raw materials, the storage of energy in man-made underground caverns, and the disposal of hazardous substances in former mines. The most serious risk with any of these usage types comes from the contact with groundwater or surface water. It causes an uncontrolled dissolution of salt rock, which in the worst case can result in the flooding or collapse of underground facilities. Especially along potash seams, cavernous structures can spread quickly, because potash salts show a much higher solubility than rock salt. However, as their chemical behavior is quite complex, previous models do not account for these highly soluble interlayers. Therefore, the objective of the present thesis is to describe the evolution of cavernous structures along potash seams in space and time in order to improve hazard mitigation during the utilization of salt deposits. The formation of cavernous structures represents an interplay of chemical and hydraulic processes. Hence, the first step is to systematically investigate the dissolution and precipitation reactions that occur when water and potash salt come into contact. For this purpose, a geochemical reaction model is used. The results show that the minerals are only partially dissolved, resulting in a porous sponge like structure. With the saturation of the solution increasing, various secondary minerals are formed, whose number and type depend on the original rock composition. Field data confirm a correlation between the degree of saturation and the distance from the center of the cavern, where solution is entering. Subsequently, the reaction model is coupled with a flow and transport code and supplemented by a novel approach called 'interchange'. The latter enables the exchange of solution and rock between areas of different porosity and mineralogy, and thus ultimately the growth of the cavernous structure. By means of several scenario analyses, cavern shape, growth rate and mineralogy are systematically investigated, taking also heterogeneous potash seams into account. The results show that basically four different cases can be distinguished, with mixed forms being a frequent occurrence in nature. The classification scheme is based on the dimensionless numbers P{\´e}clet and Damk{\"o}hler, and allows for a first assessment of the hazard potential. In future, the model can be applied to any field case, using measurement data for calibration. The presented research work provides a reactive transport model that is able to spatially and temporally characterize the propagation of cavernous structures along potash seams for the first time. Furthermore, it allows to determine thickness and composition of transition zones between cavern center and unaffected salt rock. The latter is particularly important in potash mining, so that natural cavernous structures can be located at an early stage and the risk of mine flooding can thus be reduced. The models may also contribute to an improved hazard prevention in the construction of storage caverns and the disposal of hazardous waste in salt deposits. Predictions regarding the characteristics and evolution of cavernous structures enable a better assessment of potential hazards, such as integrity or stability loss, as well as of suitable mitigation measures.},
  language  = {en}
}
@phdthesis{Zhao2021,
  author    = {Zhao, Xueru},
  title     = {Palaeoclimate and palaeoenvironment evolution from the last glacial maximum into the early holocene (23-8 ka BP) derived from Lago Grande di Monticchio sediment record (S Italy)},
  pages     = {123},
  year      = {2021},
  language  = {en}
}
@phdthesis{Jentsch2021,
  author    = {Jentsch, Anna},
  title     = {Soil gas analytics in geothermal exploration and monitoring},
  doi       = {10.25932/publishup-54403},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-544039},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxxi, 162},
  year      = {2021},
  abstract  = {Major challenges during geothermal exploration and exploitation include the structural-geological characterization of the geothermal system and the application of sustainable monitoring concepts to explain changes in a geothermal reservoir during production and/or reinjection of fluids. In the absence of sufficiently permeable reservoir rocks, faults and fracture networks are preferred drilling targets because they can facilitate the migration of hot and/or cold fluids. In volcanic-geothermal systems considerable amounts of gas emissions can be released at the earth surface, often related to these fluid-releasing structures. In this thesis, I developed and evaluated different methodological approaches and measurement concepts to determine the spatial and temporal variation of several soil gas parameters to understand the structural control on fluid flow. In order to validate their potential as innovative geothermal exploration and monitoring tools, these methodological approaches were applied to three different volcanic-geothermal systems. At each site an individual survey design was developed regarding the site-specific questions. The first study presents results of the combined measurement of CO2 flux, ground temperatures, and the analysis of isotope ratios (δ13CCO2, 3He/4He) across the main production area of the Los Humeros geothermal field, to identify locations with a connection to its supercritical (T > 374◦C and P > 221 bar) geothermal reservoir. The results of the systematic and large-scale (25 x 200 m) CO2 flux scouting survey proved to be a fast and flexible way to identify areas of anomalous degassing. Subsequent sampling with high resolution surveys revealed the actual extent and heterogenous pattern of anomalous degassing areas. They have been related to the internal fault hydraulic architecture and allowed to assess favourable structural settings for fluid flow such as fault intersections. Finally, areas of unknown structurally controlled permeability with a connection to the superhot geothermal reservoir have been determined, which represent promising targets for future geothermal exploration and development. In the second study, I introduce a novel monitoring approach by examining the variation of CO2 flux to monitor changes in the reservoir induced by fluid reinjection. For that reason, an automated, multi-chamber CO2 flux system was deployed across the damage zone of a major normal fault crossing the Los Humeros geothermal field. Based on the results of the CO2 flux scouting survey, a suitable site was selected that had a connection to the geothermal reservoir, as identified by hydrothermal CO2 degassing and hot ground temperatures (> 50 °C). The results revealed a response of gas emissions to changes in reinjection rates within 24 h, proving an active hydraulic communication between the geothermal reservoir and the earth surface. This is a promising monitoring strategy that provides nearly real-time and in-situ data about changes in the reservoir and allows to timely react to unwanted changes (e.g., pressure decline, seismicity). The third study presents results from the Aluto geothermal field in Ethiopia where an area-wide and multi-parameter analysis, consisting of measurements of CO2 flux, 222Rn, and 220Rn activity concentrations and ground temperatures was conducted to detect hidden permeable structures. 222Rn and 220Rn activity concentrations are evaluated as a complementary soil gas parameter to CO2 flux, to investigate their potential to understand tectono-volcanic degassing. The combined measurement of all parameters enabled to develop soil gas fingerprints, a novel visualization approach. Depending on the magnitude of gas emissions and their migration velocities the study area was divided in volcanic (heat), tectonic (structures), and volcano-tectonic dominated areas. Based on these concepts, volcano-tectonic dominated areas, where hot hydrothermal fluids migrate along permeable faults, present the most promising targets for future geothermal exploration and development in this geothermal field. Two of these areas have been identified in the south and south-east which have not yet been targeted for geothermal exploitation. Furthermore, two unknown areas of structural related permeability could be identified by 222Rn and 220Rn activity concentrations. Eventually, the fourth study presents a novel measurement approach to detect structural controlled CO2 degassing, in Ngapouri geothermal area, New Zealand. For the first time, the tunable diode laser (TDL) method was applied in a low-degassing geothermal area, to evaluate its potential as a geothermal exploration method. Although the sampling approach is based on profile measurements, which leads to low spatial resolution, the results showed a link between known/inferred faults and increased CO2 concentrations. Thus, the TDL method proved to be a successful in the determination of structural related permeability, also in areas where no obvious geothermal activity is present. Once an area of anomalous CO2 concentrations has been identified, it can be easily complemented by CO2 flux grid measurements to determine the extent and orientation of the degassing segment. With the results of this work, I was able to demonstrate the applicability of systematic and area-wide soil gas measurements for geothermal exploration and monitoring purposes. In particular, the combination of different soil gases using different measurement networks enables the identification and characterization of fluid-bearing structures and has not yet been used and/or tested as standard practice. The different studies present efficient and cost-effective workflows and demonstrate a hands-on approach to a successful and sustainable exploration and monitoring of geothermal resources. This minimizes the resource risk during geothermal project development. Finally, to advance the understanding of the complex structure and dynamics of geothermal systems, a combination of comprehensive and cutting-edge geological, geochemical, and geophysical exploration methods is essential.},
  language  = {en}
}
@phdthesis{Hebert2021,
  author    = {H{\´e}bert, Raphaёl},
  title     = {Investigation of vegetation and terrestrial climate variablity during the holocene},
  school      = {Universit{\"a}t Potsdam},
  pages     = {201},
  year      = {2021},
  language  = {en}
}
@phdthesis{Riedl2021,
  author    = {Riedl, Simon},
  title     = {Active tectonics in the Kenya Rift},
  doi       = {10.25932/publishup-53855},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-538552},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 207},
  year      = {2021},
  abstract  = {Magmatische und tektonisch aktive Grabenzonen (Rifts) stellen die Vorstufen entstehender Plattengrenzen dar. Diese sich spreizenden tektonischen Provinzen zeichnen sich durch allgegenw{\"a}rtige Abschiebungen aus, und die r{\"a}umliche Verteilung, die Geometrie, und das Alter dieser Abschiebungen l{\"a}sst R{\"u}ckschl{\"u}sse auf die r{\"a}umlichen und zeitlichen Zusammenh{\"a}nge zwischen tektonischer Deformation, Magmatismus und langwelliger Krustendeformation in Rifts zu. Diese Arbeit konzentriert sich auf die St{\"o}rungsaktivit{\"a}t im Kenia-Rift des k{\"a}nozoischen Ostafrikanischen Grabensystems im Zeitraum zwischen dem mittleren Pleistoz{\"a}n und dem Holoz{\"a}n. Um die fr{\"u}hen Stadien der Entstehung kontinentaler Plattengrenzen zu untersuchen, wird in dieser Arbeit eine zeitlich gemittelte minimale Extensionsrate f{\"u}r den inneren Graben des N{\"o}rdlichen Kenia-Rifts (NKR) f{\"u}r die letzten 0,5 Mio Jahre abgeleitet. Die Analyse beruht auf Messungen mit Hilfe des digitalen TanDEM-X-H{\"o}henmodells, um die Abschiebungen entlang der vulkanisch-tektonischen Achse des inneren Grabens des NKR zu kartieren und deren Versatzbetr{\"a}ge zu bestimmen. Mithilfe von vorhandenen Geochronologiedaten der deformierten vulkanischen Einheiten sowie in dieser Arbeit erstellten ⁴⁰Ar/³⁹Ar-Datierungen werden zeitlich gemittelte Extensionsraten berechnet. Die Auswertungen zeigen, dass im inneren Graben des NKR die langfristige Extensionsrate f{\"u}r mittelpleistoz{\"a}ne bis rezente St{\"o}rungen Mindestwerte von 1,0 bis 1,6 mm yr⁻¹ aufweist und lokal allerdings auch Werte bis zu 2,0 mm yr⁻¹ existieren. In Anbetracht der nahezu inaktiven Randst{\"o}rungen des NKR zeigt sich somit, dass sich die Extension auf die Region der aktiven vulkanisch-tektonischen Achse im inneren Graben konzentriert und somit ein fortgeschrittenes Stadium kontinentaler Extensionsprozesse im NKR vorliegt. In dieser Arbeit wird diese r{\"a}umlich fokussierte Extension zudem im Rahmen einer St{\"o}rungsanalyse der j{\"u}ngsten vulkanischen Erscheinungen des Kenia-Rifts betrachtet. Die Arbeit analysiert mithilfe von Gel{\"a}ndekartierungen und eines auf Luftbildern basierenden Gel{\"a}ndemodells die St{\"o}rungscharakteristika der etwa 36 tausend Jahre alten Menengai-Kaldera und der umliegenden Gebiete im zentralen Kenia-Rift. Im Allgemeinen sind die holoz{\"a}nen St{\"o}rungen innerhalb des Rifts reine, NNO-streichende Abschiebungen, die somit das gegenw{\"a}rtige tektonische Spannungsfeld wiederspiegeln; innerhalb der Menengai-Kaldera sind die jungen Strukturen jedoch von andauernder magmatischer Aktivit{\"a}t und von Aufdomung {\"u}berpr{\"a}gt. Die Kaldera befindet sich im Zentrum eines sich aktiv dehnenden Riftsegments und zusammen mit den anderen quart{\"a}ren Vulkanen des Kenia-Rifts lassen sich diese Bereiche als Kernpunkte der extensionalen St{\"o}rungsaktivit{\"a}t verstehen, die letztlich zu einer weiter entwickelten Phase magmengest{\"u}tzter Kontinentalseparation f{\"u}hren werden. Die bereits seit dem Terti{\"a}r andauernde St{\"o}rungsaktivit{\"a}t im Kenia-Rift f{\"u}hrt zur Zergliederung der gr{\"o}ßeren Rift-Senken in kleinere Segmente und beeinflusst die Sedimentologie und die Hydrologie dieser Riftbecken. Gegenw{\"a}rtig sind die meisten, durch St{\"o}rungen begrenzten Becken des Kenia-Rifts hydrologisch isoliert, sie waren aber w{\"a}hrend feuchter Klimaphasen hydrologisch miteinander verbunden; in dieser Arbeit untersuche ich deshalb auch diese hydrologische Verbindung der Rift-Becken f{\"u}r die Zeit der Afrikanischen Feuchteperiode des fr{\"u}hen Holoz{\"a}ns. Mithilfe der Analyse von digitalen Gel{\"a}ndemodellen, unter Ber{\"u}cksichtigung von geomorphologischen Anzeigern f{\"u}r Seespiegelhochst{\"a}nde, Radiokarbondatierungen und einer {\"U}bersicht {\"u}ber Fossiliendaten konnten zwei kaskadierende Flusssysteme aus diesen Daten abgeleitet werden: eine Flusskaskade in Richtung S{\"u}den und eine in Richtung Norden. Beide Kaskaden haben die derzeit isolierten Becken w{\"a}hrend des fr{\"u}hen Holoz{\"a}ns durch {\"u}berlaufende Seen und eingeschnittene Schluchten miteinander verbunden. Diese hydrologische Verbindung f{\"u}hrte zu der Ausbreitung aquatischer Fauna entlang des Rifts, und gleichzeitig stellte die Wasserscheide zwischen den beiden Flusssystemen den einzigen terrestrischen Ausbreitungskorridor dar, der eine {\"U}berquerung des Kenia-Rifts erm{\"o}glichte. Diese tektonisch-geomorphologische Rekonstruktion erkl{\"a}rt die heute isolierten Vorkommen nilotischer Fischarten in den Riftseen Kenias sowie die isolierten Vorkommen Guineo-Congolischer S{\"a}ugetiere in W{\"a}ldern {\"o}stlich des Kenia-Rifts, die sich {\"u}ber die Wasserscheide im Kenia-Rift ausbreiten konnten. Auf l{\"a}ngeren Zeitskalen sind solche Phasen hydrologischer Verbindung und Phasen der Isolation wiederholt aufgetreten und zeigen sich in wechselnden pal{\"a}o{\"o}kologischen Indikatoren in Sedimentbohrkernen. Hier stelle ich einen Sedimentbohrkern aus dem Koora-Becken des S{\"u}dlichen Kenia-Rifts vor, der einen Datensatz der Pal{\"a}o-Umweltbedingungen der letzten 1 Million Jahre beinhaltet. Dieser Datensatz zeigt, dass etwa vor 400 tausend Jahren die zuvor relativ stabilen Umweltbedingungen zum Erliegen kamen und tektonische, hydrologische und {\"o}kologische Ver{\"a}nderungen dazu f{\"u}hrten, dass die Wasserverf{\"u}gbarkeit, die Grasland-Vergesellschaftungen und die Bedeckung durch Baumvegetation zunehmend st{\"a}rkeren und h{\"a}ufigeren Schwankungen unterlagen. Diese großen Ver{\"a}nderungen fallen zeitlich mit Phasen zusammen, in denen das s{\"u}dliche Becken des Kenia-Rifts von vulkanischer und tektonischer Aktivit{\"a}t besonders betroffen war. Die vorliegende Arbeit zeigt deshalb deutlich, inwiefern die tektonischen und geomorphologischen Gegebenheiten im Zuge einer zeitlich langanhaltenden Extension die Hydrologie, die Pal{\"a}o-Umweltbedingungen sowie die Biodiversit{\"a}t einer Riftzone beeinflussen k{\"o}nnen.},
  language  = {en}
}
@phdthesis{Arnous2021,
  author    = {Arnous, Ahmad},
  title     = {Paleosismolog{\´i}a y neotect{\´o}nica del antepa{\´i}s fragmentado en el extremo sureste del Sistema Santa B{\´a}rbara, Noroeste Argentino},
  doi       = {10.25932/publishup-53527},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-535274},
  school      = {Universit{\"a}t Potsdam},
  pages     = {182},
  year      = {2021},
  abstract  = {This thesis constitutes a multidisciplinary study of the central sector of the Santa B{\´a}rbara System geological province, the tectonically active broken foreland of the central Andes of north-western Argentina. The study is based on a tectono-geomorphic characterization combined with a variety of geophysical and structural studies. The principal focus was on the faulted piedmont regions of the Sierra de La Candelaria and, to a lesser degree, the extreme south of the intermontane Met{\´a}n basin. The study region is located in the border area between the provinces of Salta and Tucum{\´a}n. The main objective was to characterize and analyze evidence of Quaternary tectonic activity in the region, in order to increase the available information on neotectonic structures and their seismogenic potential. To this end, several methods were applied and integrated, such as the interpretation of seismic reflection lines, the creation of structural sections and kinematic modeling, as well as near-surface geophysical methods, in order to explore the geometry of faults observed at the surface and to assess the behavior of potential blind faults. In a first step, a geomorphic and structural survey of the study area was carried out using LANDSAT and SENTINEL 2 multispectral satellite images, which allowed to recognize different levels of Quaternary alluvial fans and fluvial terraces that are important strain markers in the field. In a second step, different morphometric indexes were determined from digital elevation models (DEM) and combined with field observations; it was possible to identify evidence of tectonic deformation related to four neotectonic faults. In a third step, three structures (Arias, El Quemado and Copo Quile faults) were selected for more detailed studies involving Electrical Resistive Tomography (ERT) and Seismic Refraction Tomography (SRT). This part of the study enabled me to define the geometry of faults at depth, helped to infer geometric and kinematic characteristics, and confirmed the extent of recent deformation. The Arias and El Quemado faults were interpreted as reverse faults related to layer-parallel, flexuralslip faulting, while the Copo Quile fault was interpreted as a blind reverse fault. Subsequently, a joint interpretation of seismic reflection lines and well-logs from the Choromoro and Met{\´a}n basins was carried out, to decipher the principal structures and their influence on the deformation of the different sedimentary units in the intermontane basins. The obtained information was integrated into a kinematic model. This model suggests that the recent deformation is driven by a blind, deep-seated reverse fault, located under the Sierra de La Candelaria and Cantero anticline. The corresponding shortening involves the sedimentary strata of the Salta and Or{\´a}n groups in the adjacent basins, which was accommodated by faults that moved along stratal boundaries, thus bending and folding the Quaternary deposits at the surface. The kinematic model enabled identifying the approximate location of the important detachment horizons that control the overall crustal deformation style in this region. The shallowest detachment horizon is located at 4 km depth and controls deformation in a thin-skinned manner. In addition, the horizon of the thick-skinned style of deformation was identified at 21 km depth. Finally, from the integration of all the results obtained, the seismogenic potential of the faults in the study area was evaluated. The first-order faults that control deformation in the area are responsible for the large earthquakes. While, Quaternary flexural-slip faults affecting only the sedimentary cover are secondary structures that accommodate deformation and were activated very low magnitude earthquakes and/or aseismic movements. In conclusion, the results of this study allow to demonstrate that the regional fault system of intrabasinal faults in the Santa B{\´a}rbara System constitutes a potential seismogenic source in the region, where numerous towns and extensive civilian infrastructure are located. In addition, the derived kinematic model requires the existence of numerous blind structures. Only for a small number of these their presence can be unambiguously detected at the surface by geomorphic analysis, which emphasizes the need of conducting this type of studies in tectonically active regions such as the Santa B{\´a}rbara System.},
  language  = {es}
}
@phdthesis{FigueroaVillegas2021,
  author    = {Figueroa Villegas, Sara},
  title     = {Paleolagos cuaternarios como marcadores neotect{\´o}nicos, Valle de Cafayate, Cordillera Oriental (no de Argentina)},
  doi       = {10.25932/publishup-53174},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-531742},
  school      = {Universit{\"a}t Potsdam},
  pages     = {192},
  year      = {2021},
  abstract  = {The eastern flank of the southern Central Andes in north-western Argentina (NWA) is characterized by fault-bounded mountain ranges arranged in a thick-skinned active contractional orogen with a non-systematic spatiotemporal pattern of tectonic activity. This pattern is represented by instrumentally recorded crustal seismic activity as well as the distribution of Quaternary deformation phenomena along the Eastern Cordillera and the Santa B{\´a}rbara System morphotectonic provinces, creating a wide (> 200km) deformation zone that lacks a clear deformation front. The study of the neotectonic activity in this region has become more detailed over the past years and has involved morphotectonic analysis, remote sensing, geodesy, and field-based structural studies. Lacustrine deposits in the intermontane basins of the Eastern Cordillera that are exposed in areas associated with Quaternary faulting - due to their original horizontality of the fine-grained layers, are excellent strain markers to assess neotectonic activity. I analyzed lacustrine deposits that outcrop in the central area of the Calchaqu{\´i} valleys (Cafayate sector) to understand how deformation is accommodated in one of the largest intermontane basins of the tectonically active orogen. The strike of the Quaternary structures in the studied area is parallel to subparallel to the valley-bounding faults. With the stratigraphic, morphotectonic and structural study of the lacustrine deposits, I identified a minimum of five deformation episodes that affected the Quaternary stratigraphic section. Based on this I present Late Pleistocene minimum and maximum shortening rates for the central Calchaqu{\´i} intermontane valley that range between 0,19-4,47 mm/yr, respectively. The rates presented are based on balanced geological cross sections and geochronological ages obtained in this study as well as compilations from previously published studies. In order to compare the local shortening results at regional and different temporal scales, I additionally compiled Global Positioning System data from northwest Argentina to generate a surface-velocitiy profile. The results reveal a gradual decrease in horizontal surface velocities from the Eastern Cordillera toward the foreland, indicating tectonic activity in the interior of the orogen, which is recorded by seismic activity and the wide distribution of Quaternary faults and folds. In addition to the neotectonic investigation carried out in the study area, the stratigraphic analysis of the lacustrine deposits allowed to have a better understanding of the Quaternary basin evolution of the central area of the Calchaqu{\´i} valleys. At least seven distinct lacustrine deposits could be identified that correspond to an impoundment of the fluvial system and ensuing base-level changes, resulting in successive aggradation and subsequent erosion events. Together with a hydrological model previously published for the study area, the maximum elevations that the paleolakes reached were furthermore reviewed and compared with regional paleoclimate data to allow local climatic inferences. The results of this thesis are a significant contribution to our understanding of the Quaternary tectonic and the stratigraphic evolution of the central sector of the Calchaqu{\´i} valleys. Furthermore, the integration of local structural and geochronological data with regional structural and geodetic observations contributes to our knowledge of the deformation dynamics of the thick-skinned orogenic wedge of northwest Argentina.},
  language  = {es}
}
@phdthesis{vanderVeen2021,
  author    = {van der Veen, Iris},
  title     = {Defining moisture sources and (palaeo)environmental conditions using isotope geochemistry in the NW Himalaya},
  doi       = {10.25932/publishup-51439},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-514397},
  school      = {Universit{\"a}t Potsdam},
  pages     = {152},
  year      = {2021},
  abstract  = {Anthropogenic climate change alters the hydrological cycle. While certain areas experience more intense precipitation events, others will experience droughts and increased evaporation, affecting water storage in long-term reservoirs, groundwater, snow, and glaciers. High elevation environments are especially vulnerable to climate change, which will impact the water supply for people living downstream. The Himalaya has been identified as a particularly vulnerable system, with nearly one billion people depending on the runoff in this system as their main water resource. As such, a more refined understanding of spatial and temporal changes in the water cycle in high altitude systems is essential to assess variations in water budgets under different climate change scenarios. However, not only anthropogenic influences have an impact on the hydrological cycle, but changes to the hydrological cycle can occur over geological timescales, which are connected to the interplay between orogenic uplift and climate change. However, their temporal evolution and causes are often difficult to constrain. Using proxies that reflect hydrological changes with an increase in elevation, we can unravel the history of orogenic uplift in mountain ranges and its effect on the climate. In this thesis, stable isotope ratios (expressed as δ2H and δ18O values) of meteoric waters and organic material are combined as tracers of atmospheric and hydrologic processes with remote sensing products to better understand water sources in the Himalayas. In addition, the record of modern climatological conditions based on the compound specific stable isotopes of leaf waxes (δ2Hwax) and brGDGTs (branched Glycerol dialkyl glycerol tetraethers) in modern soils in four Himalayan river catchments was assessed as proxies of the paleoclimate and (paleo-) elevation. Ultimately, hydrological variations over geological timescales were examined using δ13C and δ18O values of soil carbonates and bulk organic matter originating from sedimentological sections from the pre-Siwalik and Siwalik groups to track the response of vegetation and monsoon intensity and seasonality on a timescale of 20 Myr. I find that Rayleigh distillation, with an ISM moisture source, mainly controls the isotopic composition of surface waters in the studied Himalayan catchments. An increase in d-excess in the spring, verified by remote sensing data products, shows the significant impact of runoff from snow-covered and glaciated areas on the surface water isotopic values in the timeseries. In addition, I show that biomarker records such as brGDGTs and δ2Hwax have the potential to record (paleo-) elevation by yielding a significant correlation with the temperature and surface water δ2H values, respectively, as well as with elevation. Comparing the elevation inferred from both brGDGT and δ2Hwax, large differences were found in arid sections of the elevation transects due to an additional effect of evapotranspiration on δ2Hwax. A combined study of these proxies can improve paleoelevation estimates and provide recommendations based on the results found in this study. Ultimately, I infer that the expansion of C4 vegetation between 20 and 1 Myr was not solely dependent on atmospheric pCO2, but also on regional changes in aridity and seasonality from to the stable isotopic signature of the two sedimentary sections in the Himalaya (east and west). This thesis shows that the stable isotope chemistry of surface waters can be applied as a tool to monitor the changing Himalayan water budget under projected increasing temperatures. Minimizing the uncertainties associated with the paleo-elevation reconstructions were assessed by the combination of organic proxies (δ2Hwax and brGDGTs) in Himalayan soil. Stable isotope ratios in bulk soil and soil carbonates showed the evolution of vegetation influenced by the monsoon during the late Miocene, proving that these proxies can be used to record monsoon intensity, seasonality, and the response of vegetation. In conclusion, the use of organic proxies and stable isotope chemistry in the Himalayas has proven to successfully record changes in climate with increasing elevation. The combination of δ2Hwax and brGDGTs as a new proxy provides a more refined understanding of (paleo-)elevation and the influence of climate.},
  language  = {en}
}
@phdthesis{Liu2021,
  author    = {Liu, Sisi},
  title     = {The history of plant diversity change and community assemply a high-altitude and high-latitude ecosystems inferred from sedimentary (ancient) DNA and pollen},
  school      = {Universit{\"a}t Potsdam},
  year      = {2021},
  language  = {en}
}
@phdthesis{Petersen2021,
  author    = {Petersen, Gesa Maria},
  title     = {Source studies of small earthquakes in the AlpArray: CMT inversion, seismo-tectonic analysis and methodological developments},
  doi       = {10.25932/publishup-52563},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525635},
  school      = {Universit{\"a}t Potsdam},
  pages     = {151},
  year      = {2021},
  abstract  = {Centroid moment tensor inversion can provide insight into ongoing tectonic processes and active faults. In the Alpine mountains (central Europe), challenges result from low signal-to-noise ratios of earthquakes with small to moderate magnitudes and complex wave propagation effects through the heterogeneous crustal structure of the mountain belt. In this thesis, I make use of the temporary installation of the dense AlpArray seismic network (AASN) to establish a work flow to study seismic source processes and enhance the knowledge of the Alpine seismicity. The cumulative thesis comprises four publications on the topics of large seismic networks, seismic source processes in the Alps, their link to tectonics and stress field, and the inclusion of small magnitude earthquakes into studies of active faults. Dealing with hundreds of stations of the dense AASN requires the automated assessment of data and metadata quality. I developed the open source toolbox AutoStatsQ to perform an automated data quality control. Its first application to the AlpArray seismic network has revealed significant errors of amplitude gains and sensor orientations. A second application of the orientation test to the Turkish KOERI network, based on Rayleigh wave polarization, further illustrated the potential in comparison to a P wave polarization method. Taking advantage of the gain and orientation results of the AASN, I tested different inversion settings and input data types to approach the specific challenges of centroid moment tensor (CMT) inversions in the Alps. A comparative study was carried out to define the best fitting procedures. The application to 4 years of seismicity in the Alps (2016-2019) substantially enhanced the amount of moment tensor solutions in the region. We provide a list of moment tensors solutions down to magnitude Mw 3.1. Spatial patterns of typical focal mechanisms were analyzed in the seismotectonic context, by comparing them to long-term seismicity, historical earthquakes and observations of strain rates. Additionally, we use our MT solutions to investigate stress regimes and orientations along the Alpine chain. Finally, I addressed the challenge of including smaller magnitude events into the study of active faults and source processes. The open-source toolbox Clusty was developed for the clustering of earthquakes based on waveforms recorded across a network of seismic stations. The similarity of waveforms reflects both, the location and the similarity of source mechanisms. Therefore the clustering bears the opportunity to identify earthquakes of similar faulting styles, even when centroid moment tensor inversion is not possible due to low signal-to-noise ratios of surface waves or oversimplified velocity models. The toolbox is described through an application to the Zakynthos 2018 aftershock sequence and I subsequently discuss its potential application to weak earthquakes (Mw<3.1) in the Alps.},
  language  = {en}
}
@phdthesis{Runge2021,
  author    = {Runge, Alexandra},
  title     = {Multispectral time series analyses with Landsat and Sentinel-2 to assess permafrost disturbances in North Siberia},
  doi       = {10.25932/publishup-52206},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-522062},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxiv, 134},
  year      = {2021},
  abstract  = {Permafrost is warming globally, which leads to widespread permafrost thaw and impacts the surrounding landscapes, ecosystems and infrastructure. Especially ice-rich permafrost is vulnerable to rapid and abrupt thaw, resulting from the melting of excess ground ice. Local remote sensing studies have detected increasing rates of abrupt permafrost disturbances, such as thermokarst lake change and drainage, coastal erosion and RTS in the last two decades. All of which indicate an acceleration of permafrost degradation. In particular retrogressive thaw slumps (RTS) are abrupt disturbances that expand by up to several meters each year and impact local and regional topographic gradients, hydrological pathways, sediment and nutrient mobilisation into aquatic systems, and increased permafrost carbon mobilisation. The feedback between abrupt permafrost thaw and the carbon cycle is a crucial component of the Earth system and a relevant driver in global climate models. However, an assessment of RTS at high temporal resolution to determine the dynamic thaw processes and identify the main thaw drivers as well as a continental-scale assessment across diverse permafrost regions are still lacking. In northern high latitudes optical remote sensing is restricted by environmental factors and frequent cloud coverage. This decreases image availability and thus constrains the application of automated algorithms for time series disturbance detection for large-scale abrupt permafrost disturbances at high temporal resolution. Since models and observations suggest that abrupt permafrost disturbances will intensify, we require disturbance products at continental-scale, which allow for meaningful integration into Earth system models. The main aim of this dissertation therefore, is to enhance our knowledge on the spatial extent and temporal dynamics of abrupt permafrost disturbances in a large-scale assessment. To address this, three research objectives were posed: 1. Assess the comparability and compatibility of Landsat-8 and Sentinel-2 data for a combined use in multi-spectral analysis in northern high latitudes. 2. Adapt an image mosaicking method for Landsat and Sentinel-2 data to create combined mosaics of high quality as input for high temporal disturbance assessments in northern high latitudes. 3. Automatically map retrogressive thaw slumps on the landscape-scale and assess their high temporal thaw dynamics. We assessed the comparability of Landsat-8 and Sentinel-2 imagery by spectral comparison of corresponding bands. Based on overlapping same-day acquisitions of Landsat-8 and Sentinel-2 we derived spectral bandpass adjustment coefficients for North Siberia to adjust Sentinel-2 reflectance values to resemble Landsat-8 and harmonise the two data sets. Furthermore, we adapted a workflow to combine Landsat and Sentinel-2 images to create homogeneous and gap-free annual mosaics. We determined the number of images and cloud-free pixels, the spatial coverage and the quality of the mosaic with spectral comparisons to demonstrate the relevance of the Landsat+Sentinel-2 mosaics. Lastly, we adapted the automatic disturbance detection algorithm LandTrendr for large-scale RTS identification and mapping at high temporal resolution. For this, we modified the temporal segmentation algorithm for annual gradual and abrupt disturbance detection to incorporate the annual Landsat+Sentinel-2 mosaics. We further parametrised the temporal segmentation and spectral filtering for optimised RTS detection, conducted further spatial masking and filtering, and implemented a binary object classification algorithm with machine-learning to derive RTS from the LandTrendr disturbance output. We applied the algorithm to North Siberia, covering an area of 8.1 x 106 km2. The spectral band comparison between same-day Landsat-8 and Sentinel-2 acquisitions already showed an overall good fit between both satellite products. However, applying the acquired spectral bandpass coefficients for adjustment of Sentinel-2 reflectance values, resulted in a near-perfect alignment between the same-day images. It can therefore be concluded that the spectral band adjustment succeeds in adjusting Sentinel-2 spectral values to those of Landsat-8 in North Siberia. The number of available cloud-free images increased steadily between 1999 and 2019, especially intensified after 2016 with the addition of Sentinel-2 images. This signifies a highly improved input database for the mosaicking workflow. In a comparison of annual mosaics, the Landsat+Sentinel-2 mosaics always fully covered the study areas, while Landsat-only mosaics contained data-gaps for the same years. The spectral comparison of input images and Landsat+Sentinel-2 mosaic showed a high correlation between the input images and the mosaic bands, testifying mosaicking results of high quality. Our results show that especially the mosaic coverage for northern, coastal areas was substantially improved with the Landsat+Sentinel-2 mosaics. By combining data from both Landsat and Sentinel-2 sensors we reliably created input mosaics at high spatial resolution for comprehensive time series analyses. This research presents the first automatically derived assessment of RTS distribution and temporal dynamics at continental-scale. In total, we identified 50,895 RTS, primarily located in ice-rich permafrost regions, as well as a steady increase in RTS-affected areas between 2001 and 2019 across North Siberia. From 2016 onward the RTS area increased more abruptly, indicating heightened thaw slump dynamics in this period. Overall, the RTS-affected area increased by 331 \% within the observation period. Contrary to this, five focus sites show spatiotemporal variability in their annual RTS dynamics, alternating between periods of increased and decreased RTS development. This suggests a close relationship to varying thaw drivers. The majority of identified RTS was active from 2000 onward and only a small proportion initiated during the assessment period. This highlights that the increase in RTS-affected area was mainly caused by enlarging existing RTS and not by newly initiated RTS. Overall, this research showed the advantages of combining Landsat and Sentinel-2 data in northern high latitudes and the improvements in spatial and temporal coverage of combined annual mosaics. The mosaics build the database for automated disturbance detection to reliably map RTS and other abrupt permafrost disturbances at continental-scale. The assessment at high temporal resolution further testifies the increasing impact of abrupt permafrost disturbances and likewise emphasises the spatio-temporal variability of thaw dynamics across landscapes. Obtaining such consistent disturbance products is necessary to parametrise regional and global climate change models, for enabling an improved representation of the permafrost thaw feedback.},
  language  = {en}
}
@phdthesis{Stuff2021,
  author    = {Stuff, Maria},
  title     = {Iron isotope fractionation in carbonatite melt systems},
  doi       = {10.25932/publishup-51992},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-519928},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 137},
  year      = {2021},
  abstract  = {Carbonatite magmatism is a highly efficient transport mechanism from Earth's mantle to the crust, thus providing insights into the chemistry and dynamics of the Earth's mantle. One evolving and promising tool for tracing magma interaction are stable iron isotopes, particularly because iron isotope fractionation is controlled by oxidation state and bonding environment. Meanwhile, a large data set on iron isotope fractionation in igneous rocks exists comprising bulk rock compositions and fractionation between mineral groups. Iron isotope data from natural carbonatite rocks are extremely light and of remarkably high variability. This resembles iron isotope data from mantle xenoliths, which are characterized by a variability in δ56Fe spanning three times the range found in basalts, and by the extremely light values of some whole rock samples, reaching δ56Fe as low as -0.69  per mille in a spinel lherzolite. Cause to this large range of variations may be metasomatic processes, involving metasomatic agents like volatile bearing high-alkaline silicate melts or carbonate melts. The expected effects of metasomatism on iron isotope fractionation vary with parameters like melt/rock-ratio, reaction time, and the nature of metasomatic agents and mineral reactions involved. An alternative or additional way to enrich light isotopes in the mantle could be multiple phases of melt extraction. To interpret the existing data sets more knowledge on iron isotope fractionation factors is needed. To investigate the behavior of iron isotopes in the carbonatite systems, kinetic and equilibration experiments in natro-carbonatite systems between immiscible silicate and carbonate melts were performed in an internally heated gas pressure vessel at intrinsic redox conditions at temperatures between 900 and 1200 °C and pressures of 0.5 and 0.7 GPa. The iron isotope compositions of coexisting silicate melt and carbonate melt were analyzed by solution MC-ICP-MS. The kinetic experiments employing a Fe-58 spiked starting material show that isotopic equilibrium is obtained after 48 hours. The experimental studies of equilibrium iron isotope fractionation between immiscible silicate and carbonate melts have shown that light isotopes are enriched in the carbonatite melt. The highest Δ56Fesil.m.-carb.melt (mean) of 0.13  per mille was determined in a system with a strongly peralkaline silicate melt composition (ASI ≥ 0.21, Na/Al ≤ 2.7). In three systems with extremely peralkaline silicate melt compositions (ASI between 0.11 and 0.14) iron isotope fractionation could analytically not be resolved. The lowest Δ56Fesil.m.-carb.melt (mean) of 0.02  per mille was determined in a system with an extremely peralkaline silicate melt composition (ASI ≤ 0.11 , Na/Al ≥ 6.1). The observed iron isotope fractionation is most likely governed by the redox conditions of the system. Yet, in the systems, where no fractionation occurred, structural changes induced by compositional changes possibly overrule the influence of redox conditions. This interpretation implicates, that the iron isotope system holds the potential to be useful not only for exploring redox conditions in magmatic systems, but also for discovering structural changes in a melt. In situ iron isotope analyses by femtosecond laser ablation coupled to MC-ICP-MS on magnetite and olivine grains were performed to reveal variations in iron isotope composition on the micro scale. The investigated sample is a melilitite bomb from the Salt Lake Crater group at Honolulu (Oahu, Hawaii), showing strong evidence for interaction with a carbonatite melt. While magnetite grains are rather homogeneous in their iron isotope compositions, olivine grains span a far larger range in iron isotope ratios. The variability of δ56Fe in magnetite is limited from - 0.17  per mille (± 0.11  per mille, 2SE) to +0.08  per mille (± 0.09  per mille, 2SE). δ56Fe in olivine range from -0.66 per mille (± 0.11  per mille, 2SE) to +0.10  per mille (± 0.13  per mille, 2SE). Olivine and magnetite grains hold different informations regarding kinetic and equilibrium fractionation due to their different Fe diffusion coefficients. The observations made in the experiments and in the in situ iron isotope analyses suggest that the extremely light iron isotope signatures found in carbonatites are generated by several steps of isotope fractionation during carbonatite genesis. These may involve equilibrium and kinetic fractionation. Since iron isotopic signatures in natural systems are generated by a combination of multiple factors (pressure, temperature, redox conditions, phase composition and structure, time scale), multi tracer approaches are needed to explain signatures found in natural rocks.},
  language  = {en}
}
@phdthesis{Barrionuevo2020,
  author    = {Barrionuevo, Mat{\´i}as},
  title     = {The role of the upper plate in the Andean tectonic evolution (33-36°S): insights from structural geology and numerical modeling},
  doi       = {10.25932/publishup-51590},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-515909},
  school      = {Universit{\"a}t Potsdam},
  pages     = {148, S2},
  year      = {2020},
  abstract  = {Los Andes Centrales del Sur (33-36°S) son un gran laboratorio para el estudio de los procesos de deformaci{\´o}n orog{\´e}nica, donde las condiciones de borde, como la geometr{\´i}a de la placa subductada, imponen un importante control sobre la deformaci{\´o}n andina. Por otro lado, la Placa Sudamericana presenta una serie de heterogeneidades que tambi{\´e}n imparten un control sobre el modo de deformaci{\´o}n. El objetivo de esta tesis es probar el control de este {\´u}ltimo factor sobre la construcci{\´o}n del sistema orog{\´e}nico andino. A partir de la integraci{\´o}n de la informaci{\´o}n superficial y de subsuelo en el {\´a}rea sur (34°-36°S), se estudi{\´o} la evoluci{\´o}n de la deformaci{\´o}n andina sobre el segmento de subducci{\´o}n normal. Se desarroll{\´o} un modelo estructural que eval{\´u}a el estado de esfuerzos desde el Mioceno hasta la actualidad, el rol de estructuras previas y su influencia en la migraci{\´o}n de fluidos. Con estos datos y publicaciones previas de la zona norte del {\´a}rea de estudio (33°-34ºS), se realiz{\´o} un modelado num{\´e}rico geodin{\´a}mico para probar la hip{\´o}tesis del papel de las heterogeneidades de la placa superior en la evoluci{\´o}n andina. Se utilizaron dos c{\´o}digos (LAPEX-2D y ASPECT) basados en elementos finitos/diferencias finitas, que simulan el comportamiento de materiales con reolog{\´i}as elastoviscopl{\´a}sticas bajo deformaci{\´o}n. Los resultados del modelado sugieren que la deformaci{\´o}n contraccional de la placa superior est{\´a} significativamente controlada por la resistencia de la lit{\´o}sfera, que est{\´a} definida por la composici{\´o}n de la corteza superior e inferior y por la proporci{\´o}n del manto litosf{\´e}rico, que a su vez est{\´a} definida por eventos tect{\´o}nicos previos. Estos eventos previos tambi{\´e}n definieron la composici{\´o}n de la corteza y su geometr{\´i}a, que es otro factor que controla la localizaci{\´o}n de la deformaci{\´o}n. Con una composici{\´o}n de corteza inferior m{\´a}s f{\´e}lsica, la deformaci{\´o}n sigue un modo de cizalla pura mientras que las composiciones m{\´a}s m{\´a}ficas provocan un modo de deformaci{\´o}n tipo cizalla simple. Por otro lado, observamos que el espesor inicial de la lit{\´o}sfera controla la localizaci{\´o}n de la deformaci{\´o}n, donde zonas con lit{\´o}sfera m{\´a}s fina es propensa a concentrar la deformaci{\´o}n. Un l{\´i}mite lit{\´o}sfera-asten{\´o}sfera asim{\´e}trico, como resultado del flujo de la cu{\~n}a mant{\´e}lica tiende a generar despegues vergentes al E.},
  language  = {en}
}
@phdthesis{RuizMonroy2021,
  author    = {Ruiz-Monroy, Ricardo},
  title     = {Organic geochemical characterization of the Yacoraite Formation (NW-Argentina)-paleoenvironment and petroleum potential},
  doi       = {10.25932/publishup-51869},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-518697},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 161},
  year      = {2021},
  abstract  = {This dissertation was carried out as part of the international and interdisciplinary graduate school StRATEGy. This group has set itself the goal of investigating geological processes that take place on different temporal and spatial scales and have shaped the southern central Andes. This study focuses on claystones and carbonates of the Yacoraite Fm. that were deposited between Maastricht and Dan in the Cretaceous Salta Rift Basin. The former rift basin is located in northwest Argentina and is divided into the sub-basins Tres Cruces, Met{\´a}n-Aleman{\´i}a and Lomas de Olmedo. The overall motivation for this study was to gain new knowledge about the evolution of marine and lacustrine conditions during the Yacoraite Fm. Deposit in the Tres Cruces and Met{\´a}n-Aleman{\´i}a sub-basins. Other important aspects that were examined within the scope of this dissertation are the conversion of organic matter from Yacoraite Fm. into oil and its genetic relationship to selected oils produced and natural oil spills. The results of my study show that the Yacoraite Fm. began to be deposited under marine conditions and that a lacustrine environment developed by the end of the deposition in the Tres Cruces and Met{\´a}n-Aleman{\´i}a Basins. In general, the kerogen of Yacoraite Fm. consists mainly of the kerogen types II, III and II / III mixtures. Kerogen type III is mainly found in samples from the Yacoraite Fm., whose TOC values are low. Due to the adsorption of hydrocarbons on the mineral surfaces (mineral matrix effect), the content of type III kerogen with Rock-Eval pyrolysis in these samples could be overestimated. Investigations using organic petrography show that the organic particles of Yacoraite Fm. mainly consist of alginites and some vitrinite-like particles. The pyrolysis GC of the rock samples showed that the Yacoraite Fm. generates low-sulfur oils with a predominantly low-wax, paraffinic-naphthenic-aromatic composition and paraffinic wax-rich oils. Small proportions of paraffinic, low-wax oils and a gas condensate-generating facies are also predicted. Here, too, mineral matrix effects were taken into account, which can lead to a quantitative overestimation of the gas-forming character. The results of an additional 1D tank modeling carried out show that the beginning (10\% TR) of the oil genesis took place between ≈10 Ma and ≈4 Ma. Most of the oil (from ≈50\% to 65\%) was generated prior to the development of structural traps formed during the Plio-Pleistocene Diaguita deformation phase. Only ≈10\% of the total oil generated was formed and potentially trapped after the formation of structural traps. Important factors in the risk assessment of this petroleum system, which can determine the small amounts of generated and migrated oil, are the generally low TOC contents and the variable thickness of the Yacoraite Fm. Additional risks are associated with a low density of information about potentially existing reservoir structures and the quality of the overburden.},
  language  = {en}
}
@phdthesis{Spooner2021,
  author    = {Spooner, Cameron},
  title     = {How does lithospheric configuration relate to deformation in the Alpine region?},
  doi       = {10.25932/publishup-51644},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-516442},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiv, 138},
  year      = {2021},
  abstract  = {Forming as a result of the collision between the Adriatic and European plates, the Alpine orogen exhibits significant lithospheric heterogeneity due to the long history of interplay between these plates, other continental and oceanic blocks in the region, and inherited features from preceeding orogenies. This implies that the thermal and rheological configuration of the lithosphere also varies significantly throughout the region. Lithology and temperature/pressure conditions exert a first order control on rock strength, principally via thermally activated creep deformation and on the distribution at depth of the brittle-ductile transition zone, which can be regarded as the lower bound to the seismogenic zone. Therefore, they influence the spatial distribution of seismicity within a lithospheric plate. In light of this, accurately constrained geophysical models of the heterogeneous Alpine lithospheric configuration, are crucial in describing regional deformation patterns. However, despite the amount of research focussing on the area, different hypotheses still exist regarding the present-day lithospheric state and how it might relate to the present-day seismicity distribution. This dissertaion seeks to constrain the Alpine lithospheric configuration through a fully 3D integrated modelling workflow, that utilises multiple geophysical techniques and integrates from all available data sources. The aim is therefore to shed light on how lithospheric heterogeneity may play a role in influencing the heterogeneous patterns of seismicity distribution observed within the region. This was accomplished through the generation of: (i) 3D seismically constrained, structural and density models of the lithosphere, that were adjusted to match the observed gravity field; (ii) 3D models of the lithospheric steady state thermal field, that were adjusted to match observed wellbore temperatures; and (iii) 3D rheological models of long term lithospheric strength, with the results of each step used as input for the following steps. Results indicate that the highest strength within the crust (~ 1 GPa) and upper mantle (> 2 GPa), are shown to occur at temperatures characteristic for specific phase transitions (more felsic crust: 200 - 400 °C; more mafic crust and upper lithospheric mantle: ~600 °C) with almost all seismicity occurring in these regions. However, inherited lithospheric heterogeneity was found to significantly influence this, with seismicity in the thinner and more mafic Adriatic crust (~22.5 km, 2800 kg m-3, 1.30E-06 W m-3) occuring to higher temperatures (~600 °C) than in the thicker and more felsic European crust (~27.5 km, 2750 kg m-3, 1.3-2.6E-06 W m-3, ~450 °C). Correlation between seismicity in the orogen forelands and lithospheric strength, also show different trends, reflecting their different tectonic settings. As such, events in the plate boundary setting of the southern foreland correlate with the integrated lithospheric strength, occurring mainly in the weaker lithosphere surrounding the strong Adriatic indenter. Events in the intraplate setting of the northern foreland, instead correlate with crustal strength, mainly occurring in the weaker and warmer crust beneath the Upper Rhine Graben. Therefore, not only do the findings presented in this work represent a state of the art understanding of the lithospheric configuration beneath the Alps and their forelands, but also a significant improvement on the features known to significantly influence the occurrence of seismicity within the region. This highlights the importance of considering lithospheric state in regards to explaining observed patterns of deformation.},
  language  = {en}
}
@phdthesis{Krstulovic2021,
  author    = {Krstulovic, Marija},
  title     = {Local structure of network formers and network modifiers in silicate melts at high pressure and temperature conditions},
  doi       = {10.25932/publishup-51641},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-516415},
  school      = {Universit{\"a}t Potsdam},
  pages     = {137},
  year      = {2021},
  abstract  = {Silikatische Schmelzen sind wichtiger Bestandteil des Erdinneren und als solche leisten sie in magmatischen Prozessen einen wesentlichen Beitrag in der Dynamik der festen Erde und der chemischen Entwicklung des gesamten Erdk{\"o}pers. Makroskopische physikalische und chemische Eigenschaften wie Dichte, Kompressibilit{\"a}t, Viskosit{\"a}t, Polymerisationsgrad etc. sind durch die atomare Struktur der Schmelzen bestimmt. In Abh{\"a}ngigkeit vom Druck, aber auch von der Temperatur und der chemischen Zusammensetzung zeigen silikatische Schmelzen unterschiedliche strukturelle Eigenschaften. Diese Eigenschaften sind am besten durch die lokale Koordinationsumgebung, d.h. Symmetrie und Anzahl der Nachbarn (Koordinationszahl) eines Atoms, sowie dem Abstand zwischen Zentralatom und Nachbarn (atomarer Abstand) beschrieben. Mit steigendem Druck und Temperatur, das heißt mit der zunehmenden Tiefe in der Erde, nimmt die Dichte der Schmelzen zu, welches zur Ver{\"a}nderung von Koordinationszahl und Abst{\"a}nden f{\"u}hren kann. Bei gleichbleibender Koordinationszahl nimmt der Abstand in der Regel zu. Kommt es zu Erh{\"o}hung der Koordinationszahl kann der Abstand zunehmen. Diese allgemeinen Trends k{\"o}nnen allerdings stark variieren, welches insbesondere auf die chemische Zusammensetzung zur{\"u}ckzuf{\"u}hren ist. Dadurch, dass nat{\"u}rliche Schmelzen der tiefen Erde f{\"u}r direkte Untersuchungen nicht zug{\"a}nglich sind, um ihre Eigenschaften unter den relevanten Bedingungen zu verstehen, wurden umfangreiche experimentelle und theoretische Untersuchungen bisher durchgef{\"u}hrt. Dies wurde h{\"a}ufig am Beispiel von amorphen Proben der Endglieder SiO2, und GeO2 studiert, wobei letzteres als strukturelles und chemisches Analogmodell zu SiO2 dient. Meistens wurden die Experimente bei hohem Druck und bei Raumtemperatur durchgef{\"u}hrt. Nat{\"u}rliche Schmelzen sind chemisch deutlich komplexer als die einfachen Endglieder SiO2 und GeO2, so dass die Beobachtungen an diesen m{\"o}glicherweise zu falschen Verdichtungsmodellen f{\"u}hren k{\"o}nnen. Weiterhin k{\"o}nnen die Untersuchungen an Gl{\"a}sern bei Raumtemperatur potentiell starke Abweichungen zu Eigenschaften von Schmelzen bei nat{\"u}rlichen thermodynamischen Bedingungen aufweisen. Das Ziel dieser Dissertation war es zu erl{\"a}utern, welchen Einfluss die Zusammensetzung und die Temperatur auf die strukturelle Eigenschaften der Schmelzen unter hohen Dr{\"u}cken haben. Um das zu verstehen, haben wir komplexe alumino-germanatische und alumino-silikatische Gl{\"a}ser studiert. Genauer gesagt, wir haben synthetische Gl{\"a}ser studiert, die eine Zusammensetzung wie das Mineral Albit und wie eine Mischung von Albit-Diopsid im eutektischen Punkt haben. Das Albitglas {\"a}hnelt strukturell einer vereinfachten granitischen Schmelze, w{\"a}hrend das Albit-Diopsid-Glas eine vereinfachte basaltische Schmelze simuliert. Um die lokale Koordinationsumgebung der Elemente zu studieren, haben wir die R{\"o}ntgenabsorptionsspektroskopie in Kombination mit einer Diamantstempelzelle benutzt. Dadurch, dass die Diamanten eine hohe Absorption f{\"u}r R{\"o}ntgenstrahlung mit Energien unterhalb von 10 keV aufweisen, ist die unmittelbare Untersuchung der geologisch sehr relevanten Elemente wie Si, Al, Ca, Mg etc. mit dieser Spektroskopie in Kombination mit einer Diamantstempelzelle nicht m{\"o}glich. Deswegen wurden die Gl{\"a}ser mit Ge und Sr dotiert. Diese Elemente dienen teilweise oder vollst{\"a}ndig als Ersatzelemente f{\"u}r wichtige Hauptelemente. In diesem Sinne, dient Ge als Ersatzelement f{\"u}r Si und andere Netzwerkbildner, w{\"a}hrend Sr Netzwerkwandler wie Z.B. Ca, Na, Mg etc., sowie andere Kationen mit großem Ionenradius ersetzt. Im ersten Schritt haben wir die Ge K-Kante im Ge-Albit-Glass, NaAlGe3O8, bei Raumtemperatur bis 131 GPa untersucht. Dieses Glas hat eine h{\"o}here chemische Komplexit{\"a}t als SiO2 und GeO2, aber es ist immer noch vollst{\"a}ndig polymerisiert. Die Unterschiede im Verdichtungsmechanismus zwischen diesem Glas und den einfachen Oxiden k{\"o}nnen so eindeutig auf h{\"o}here chemische Komplexit{\"a}t zur{\"u}ckgef{\"u}hrt werden. Die partiell mit Ge und Sr dotierten Albit und Albit-Diopsid-Zusammensetzungen wurden bei Raumtemperatur f{\"u}r Ge bis 164 GPa und f{\"u}r Sr bis 42 GPa untersucht. W{\"a}hrend das Albitglass wie NaAlGe3O8 nominelll vollst{\"a}ndig polymerisiert ist, ist das Albit-Diopsid Glas teilweise depolymerisiert. Die Ergebnisse zeigen, dass in allen drei Gl{\"a}sern strukturelle An̈derungen in den ersten 25 bis maximal 30 GPa stattfinden, wobei beide Ge und Sr die maximale Koordinationszahl 6 bzw. ∼9 erreichen. Bei h{\"o}heren Dr{\"u}cken findet in den Gl{\"a}sern nur eine isostrukturelle Schrumpfung der Koordinationspolyeder statt. Der wichtigste Befund der Hochdruckstudien an den alumino-silikatischen und alumino-germanatischen Gl{\"a}sern ist, dass in diesen komplexen Gl{\"a}sern die Polyeder eine viel h{\"o}here Kompressibilit{\"a}t aufweisen als bei den Endgliedern zu beobachten. Das zeigt sich insbesondere durch die starke Verk{\"u}rzung der Ge-O Abst{\"a}nde in dem amorphen NaAlGe3O8 und Albit-Diopsid-Glas bei Dr{\"u}cken {\"u}ber 30 GPa. Zus{\"a}tzlich zu den Effekten der Zusammensetzung auf den Verdichtungsprozess, haben wir den Einfluss der Temperatur auf die strukturelle {\"A}nderungen untersucht. Dazu haben wir das Albit-Diopsid-Glas untersucht, da es den Schmelzen im unteren Mantel chemisch am {\"a}hnlichsten ist. Wir haben die Ge K-Kante der Probe mit einer resistiv-geheizten und einer Laser-geheizter Diamantstempelzelle untersucht, f{\"u}r einen Druckbereich bis zu 48 GPa, sowie einen Temperaturbereich bis 5000 K. Hohe Temperaturen, bei denen die Probe fl{\"u}ssig ist und die f{\"u}r den Erdmantel relevant sind, haben einen bedeutenden Einfluss auf die strukturelle Transformation. Diese wird um ca. 30\% zu deutlich niedrigeren Dr{\"u}cken verschoben, im Vergleich zu den Gl{\"a}sern bei Raumtemperatur und unterhalb von 1000 K. Die Ergebnisse dieser Dissertation stellen einen wichtigen Beitrag fur das Verst{\"a}ndnis der Eigenschaften von Schmelzen unter Bedingungen des unteren Mantels dar. Im Kontext der Diskussion {\"u}ber die Existenz und den Ursprung von silikatischen Schmelzen mit ultrahoher Dichte, welche an der Grenze zwischen Mantel und Erdkern aufgrund seismologischer Daten vermutet werden, zeigen diese Untersuchugen, dass die im Vergleich zur Umgebung h{\"o}here Dichte nicht durch strukturelle Besonderheiten, sondern durch eine besondere chemische Zusammensetzung erkl{\"a}rt werden m{\"u}ssen. Außerdem legen die Ergebnisse nahe, dass f{\"u}r Schmelzen im unteren Erdmantel nur sehr geringe L{\"o}slichkeiten von Edelgasen zu erwarten sind, so dass die strukturellen Eigenschaften deutlich den Gesamthaushalt und Transport der Edelgase im Erdmantel beeinflussen.},
  language  = {en}
}
@phdthesis{Wetzel2021,
  author    = {Wetzel, Maria},
  title     = {Pore space alterations and their impact on hydraulic and mechanical rock properties quantified by numerical simulations},
  doi       = {10.25932/publishup-51206},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512064},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XI, 107},
  year      = {2021},
  abstract  = {Geochemical processes such as mineral dissolution and precipitation alter the microstructure of rocks, and thereby affect their hydraulic and mechanical behaviour. Quantifying these property changes and considering them in reservoir simulations is essential for a sustainable utilisation of the geological subsurface. Due to the lack of alternatives, analytical methods and empirical relations are currently applied to estimate evolving hydraulic and mechanical rock properties associated with chemical reactions. However, the predictive capabilities of analytical approaches remain limited, since they assume idealised microstructures, and thus are not able to reflect property evolution for dynamic processes. Hence, aim of the present thesis is to improve the prediction of permeability and stiffness changes resulting from pore space alterations of reservoir sandstones. A detailed representation of rock microstructure, including the morphology and connectivity of pores, is essential to accurately determine physical rock properties. For that purpose, three-dimensional pore-scale models of typical reservoir sandstones, obtained from highly resolved micro-computed tomography (micro-CT), are used to numerically calculate permeability and stiffness. In order to adequately depict characteristic distributions of secondary minerals, the virtual samples are systematically altered and resulting trends among the geometric, hydraulic, and mechanical rock properties are quantified. It is demonstrated that the geochemical reaction regime controls the location of mineral precipitation within the pore space, and thereby crucially affects the permeability evolution. This emphasises the requirement of determining distinctive porosity-permeability relationships by means of digital pore-scale models. By contrast, a substantial impact of spatial alterations patterns on the stiffness evolution of reservoir sandstones are only observed in case of certain microstructures, such as highly porous granular rocks or sandstones comprising framework-supporting cementations. In order to construct synthetic granular samples a process-based approach is proposed including grain deposition and diagenetic cementation. It is demonstrated that the generated samples reliably represent the microstructural complexity of natural sandstones. Thereby, general limitations of imaging techniques can be overcome and various realisations of granular rocks can be flexibly produced. These can be further altered by virtual experiments, offering a fast and cost-effective way to examine the impact of precipitation, dissolution or fracturing on various petrophysical correlations. The presented research work provides methodological principles to quantify trends in permeability and stiffness resulting from geochemical processes. The calculated physical property relations are directly linked to pore-scale alterations, and thus have a higher accuracy than commonly applied analytical approaches. This will considerably improve the predictive capabilities of reservoir models, and is further relevant to assess and reduce potential risks, such as productivity or injectivity losses as well as reservoir compaction or fault reactivation. Hence, the proposed method is of paramount importance for a wide range of natural and engineered subsurface applications, including geothermal energy systems, hydrocarbon reservoirs, CO2 and energy storage as well as hydrothermal deposit exploration.},
  language  = {en}
}
@phdthesis{Gholamrezaie2021,
  author    = {Gholamrezaie, Ershad},
  title     = {Variations of lithospheric strength in different tectonic settings},
  doi       = {10.25932/publishup-51146},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-511467},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 147},
  year      = {2021},
  abstract  = {Rheology describes the flow of matter under the influence of stress, and - related to solids- it investigates how solids subjected to stresses deform. As the deformation of the Earth's outer layers, the lithosphere and the crust, is a major focus of rheological studies, rheology in the geosciences describes how strain evolves in rocks of variable composition and temperature under tectonic stresses. It is here where deformation processes shape the form of ocean basins and mountain belts that ultimately result from the complex interplay between lithospheric plate motion and the susceptibility of rocks to the influence of plate-tectonic forces. A rigorous study of the strength of the lithosphere and deformation phenomena thus requires in-depth studies of the rheological characteristics of the involved materials and the temporal framework of deformation processes. This dissertation aims at analyzing the influence of the physical configuration of the lithosphere on the present-day thermal field and the overall rheological characteristics of the lithosphere to better understand variable expressions in the formation of passive continental margins and the behavior of strike-slip fault zones. The main methodological approach chosen is to estimate the present-day thermal field and the strength of the lithosphere by 3-D numerical modeling. The distribution of rock properties is provided by 3-D structural models, which are used as the basis for the thermal and rheological modeling. The structural models are based on geophysical and geological data integration, additionally constrained by 3-D density modeling. More specifically, to decipher the thermal and rheological characteristics of the lithosphere in both oceanic and continental domains, sedimentary basins in the Sea of Marmara (continental transform setting), the SW African passive margin (old oceanic crust), and the Norwegian passive margin (young oceanic crust) were selected for this study. The Sea of Marmara, in northwestern Turkey, is located where the dextral North Anatolian Fault zone (NAFZ) accommodates the westward escape of the Anatolian Plate toward the Aegean. Geophysical observations indicate that the crust is heterogeneous beneath the Marmara basin, but a detailed characterization of the lateral crustal heterogeneities is presented for the first time in this study. Here, I use different gravity datasets and the general non-uniqueness in potential field modeling, to propose three possible end-member scenarios of crustal configuration. The models suggest that pronounced gravitational anomalies in the basin originate from significant density heterogeneities within the crust. The rheological modeling reveals that associated variations in lithospheric strength control the mechanical segmentation of the NAFZ. Importantly, a strong crust that is mechanically coupled to the upper mantle spatially correlates with aseismic patches where the fault bends and changes its strike in response to the presence of high-density lower crustal bodies. Between the bends, mechanically weaker crustal domains that are decoupled from the mantle are characterized by creep. For the passive margins of SW Africa and Norway, two previously published 3-D conductive and lithospheric-scale thermal models were analyzed. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data, such as seismic observations and the gravity field. Here, the rheological modeling suggests that the present-day lithospheric strength across the oceanic domain is ultimately affected by the age and past thermal and tectonic processes as well as the depth of the thermal lithosphere-asthenosphere boundary, while the configuration of the crystalline crust dominantly controls the rheological behavior of the lithosphere beneath the continental domains of both passive margins. The thermal and rheological models show that the variations of lithospheric strength are fundamentally influenced by the temperature distribution within the lithosphere. Moreover, as the composition of the lithosphere significantly influences the present-day thermal field, it therefore also affects the rheological characteristics of the lithosphere. Overall my studies add to our understanding of regional tectonic deformation processes and the long-term behavior of sedimentary basins; they confirm other analyses that have pointed out that crustal heterogeneities in the continents result in diverse lithospheric thermal characteristics, which in turn results in higher complexity and variations of rheological behavior compared to oceanic domains with a thinner, more homogeneous crust.},
  language  = {en}
}
@phdthesis{Davis2021,
  author    = {Davis, Timothy},
  title     = {An analytical and numerical analysis of fluid-filled crack propagation in three dimensions},
  doi       = {10.25932/publishup-50960},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-509609},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 187},
  year      = {2021},
  abstract  = {Fluids in the Earth's crust can move by creating and flowing through fractures, in a process called `hydraulic fracturing'. The tip-line of such fluid-filled fractures grows at locations where stress is larger than the strength of the rock. Where the tip stress vanishes, the fracture closes and the fluid-front retreats. If stress gradients exist on the fracture's walls, induced by fluid/rock density contrasts or topographic stresses, this results in an asymmetric shape and growth of the fracture, allowing for the contained batch of fluid to propagate through the crust. The state-of-the-art analytical and numerical methods to simulate fluid-filled fracture propagation are two-dimensional (2D). In this work I extend these to three dimensions (3D). In my analytical method, I approximate the propagating 3D fracture as a penny-shaped crack that is influenced by both an internal pressure and stress gradients. In addition, I develop a numerical method to model propagation where curved fractures can be simulated as a mesh of triangular dislocations, with the displacement of faces computed using the displacement discontinuity method. I devise a rapid technique to approximate stress intensity and use this to calculate the advance of the tip-line. My 3D models can be applied to arbitrary stresses, topographic and crack shapes, whilst retaining short computation times. I cross-validate my analytical and numerical methods and apply them to various natural and man-made settings, to gain additional insights into the movements of hydraulic fractures such as magmatic dikes and fluid injections in rock. In particular, I calculate the `volumetric tipping point', which once exceeded allows a fluid-filled fracture to propagate in a `self-sustaining' manner. I discuss implications this has for hydro-fracturing in industrial operations. I also present two studies combining physical models that define fluid-filled fracture trajectories and Bayesian statistical techniques. In these studies I show that the stress history of the volcanic edifice defines the location of eruptive vents at volcanoes. Retrieval of the ratio between topographic to remote stresses allows for forecasting of probable future vent locations. Finally, I address the mechanics of 3D propagating dykes and sills in volcanic regions. I focus on Sierra Negra volcano in the Gal\'apagos islands, where in 2018, a large sill propagated with an extremely curved trajectory. Using a 3D analysis, I find that shallow horizontal intrusions are highly sensitive to topographic and buoyancy stress gradients, as well as the effects of the free surface.},
  language  = {en}
}
@phdthesis{Cheng2021,
  author    = {Cheng, Chaojie},
  title     = {Transient permeability in porous and fractured sandstones mediated by fluid-rock interactions},
  doi       = {10.25932/publishup-51012},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-510124},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIV, 148},
  year      = {2021},
  abstract  = {Understanding the fluid transport properties of subsurface rocks is essential for a large number of geotechnical applications, such as hydrocarbon (oil/gas) exploitation, geological storage (CO2/fluids), and geothermal reservoir utilization. To date, the hydromechanically-dependent fluid flow patterns in porous media and single macroscopic rock fractures have received numerous investigations and are relatively well understood. In contrast, fluid-rock interactions, which may permanently affect rock permeability by reshaping the structure and changing connectivity of pore throats or fracture apertures, need to be further elaborated. This is of significant importance for improving the knowledge of the long-term evolution of rock transport properties and evaluating a reservoir' sustainability. The thesis focuses on geothermal energy utilization, e.g., seasonal heat storage in aquifers and enhanced geothermal systems, where single fluid flow in porous rocks and rock fracture networks under various pressure and temperature conditions dominates. In this experimental study, outcrop samples (i.e., Flechtinger sandstone, an illite-bearing Lower Permian rock, and Fontainebleau sandstone, consisting of pure quartz) were used for flow-through experiments under simulated hydrothermal conditions. The themes of the thesis are (1) the investigation of clay particle migration in intact Flechtinger sandstone and the coincident permeability damage upon cyclic temperature and fluid salinity variations; (2) the determination of hydro-mechanical properties of self-propping fractures in Flechtinger and Fontainebleau sandstones with different fracture features and contrasting mechanical properties; and (3) the investigation of the time-dependent fracture aperture evolution of Fontainebleau sandstone induced by fluid-rock interactions (i.e., predominantly pressure solution). Overall, the thesis aims to unravel the mechanisms of the instantaneous reduction (i.e., direct responses to thermo-hydro-mechanical-chemical (THMC) conditions) and progressively-cumulative changes (i.e., time-dependence) of rock transport properties. Permeability of intact Flechtinger sandstone samples was measured under each constant condition, where temperature (room temperature up to 145 °C) and fluid salinity (NaCl: 0 ~ 2 mol/l) were stepwise changed. Mercury intrusion porosimetry (MIP), electron microprobe analysis (EMPA), and scanning electron microscopy (SEM) were performed to investigate the changes of local porosity, microstructures, and clay element contents before and after the experiments. The results indicate that the permeability of illite-bearing Flechtinger sandstones will be impaired by heating and exposure to low salinity pore fluids. The chemically induced permeability variations prove to be path-dependent concerning the applied succession of fluid salinity changes. The permeability decay induced by a temperature increase and a fluid salinity reduction operates by relatively independent mechanisms, i.e., thermo-mechanical and thermo-chemical effects. Further, the hydro-mechanical investigations of single macroscopic fractures (aligned, mismatched tensile fractures, and smooth saw-cut fractures) illustrate that a relative fracture wall offset could significantly increase fracture aperture and permeability, but the degree of increase depends on fracture surface roughness. X-ray computed tomography (CT) demonstrates that the contact area ratio after the pressure cycles is inversely correlated to the fracture offset. Moreover, rock mechanical properties, determining the strength of contact asperities, are crucial so that relatively harder rock (i.e., Fontainebleau sandstone) would have a higher self-propping potential for sustainable permeability during pressurization. This implies that self-propping rough fractures with a sufficient displacement are efficient pathways for fluid flow if the rock matrix is mechanically strong. Finally, two long-term flow-through experiments with Fontainebleau sandstone samples containing single fractures were conducted with an intermittent flow (~140 days) and continuous flow (~120 days), respectively. Permeability and fluid element concentrations were measured throughout the experiments. Permeability reduction occurred at the beginning stage when the stress was applied, while it converged at later stages, even under stressed conditions. Fluid chemistry and microstructure observations demonstrate that pressure solution governs the long-term fracture aperture deformation, with remarkable effects of the pore fluid (Si) concentration and the structure of contact grain boundaries. The retardation and the cessation of rock fracture deformation are mainly induced by the contact stress decrease due to contact area enlargement and a dissolved mass accumulation within the contact boundaries. This work implies that fracture closure under constant (pressure/stress and temperature) conditions is likely a spontaneous process, especially at the beginning stage after pressurization when the contact area is relatively small. In contrast, a contact area growth yields changes of fracture closure behavior due to the evolution of contact boundaries and concurrent changes in their diffusive properties. Fracture aperture and thus permeability will likely be sustainable in the long term if no other processes (e.g., mineral precipitations in the open void space) occur.},
  language  = {en}
}
@phdthesis{BayonaViveros2021,
  author    = {Bayona Viveros, Jose},
  title     = {Constructing global stationary seismicity models from the long-term balance of interseismic strain measurements and earthquake-catalog data},
  doi       = {10.25932/publishup-50927},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-509270},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 83},
  year      = {2021},
  abstract  = {One third of the world's population lives in areas where earthquakes causing at least slight damage are frequently expected. Thus, the development and testing of global seismicity models is essential to improving seismic hazard estimates and earthquake-preparedness protocols for effective disaster-risk mitigation. Currently, the availability and quality of geodetic data along plate-boundary regions provides the opportunity to construct global models of plate motion and strain rate, which can be translated into global maps of forecasted seismicity. Moreover, the broad coverage of existing earthquake catalogs facilitates in present-day the calibration and testing of global seismicity models. As a result, modern global seismicity models can integrate two independent factors necessary for physics-based, long-term earthquake forecasting, namely interseismic crustal strain accumulation and sudden lithospheric stress release. In this dissertation, I present the construction of and testing results for two global ensemble seismicity models, aimed at providing mean rates of shallow (0-70 km) earthquake activity for seismic hazard assessment. These models depend on the Subduction Megathrust Earthquake Rate Forecast (SMERF2), a stationary seismicity approach for subduction zones, based on the conservation of moment principle and the use of regional "geodesy-to-seismicity" parameters, such as corner magnitudes, seismogenic thicknesses and subduction dip angles. Specifically, this interface-earthquake model combines geodetic strain rates with instrumentally-recorded seismicity to compute long-term rates of seismic and geodetic moment. Based on this, I derive analytical solutions for seismic coupling and earthquake activity, which provide this earthquake model with the initial abilities to properly forecast interface seismicity. Then, I integrate SMERF2 interface-seismicity estimates with earthquake computations in non-subduction zones provided by the Seismic Hazard Inferred From Tectonics based on the second iteration of the Global Strain Rate Map seismicity approach to construct the global Tectonic Earthquake Activity Model (TEAM). Thus, TEAM is designed to reduce number, and potentially spatial, earthquake inconsistencies of its predecessor tectonic earthquake model during the 2015-2017 period. Also, I combine this new geodetic-based earthquake approach with a global smoothed-seismicity model to create the World Hybrid Earthquake Estimates based on Likelihood scores (WHEEL) model. This updated hybrid model serves as an alternative earthquake-rate approach to the Global Earthquake Activity Rate model for forecasting long-term rates of shallow seismicity everywhere on Earth. Global seismicity models provide scientific hypotheses about when and where earthquakes may occur, and how big they might be. Nonetheless, the veracity of these hypotheses can only be either confirmed or rejected after prospective forecast evaluation. Therefore, I finally test the consistency and relative performance of these global seismicity models with independent observations recorded during the 2014-2019 pseudo-prospective evaluation period. As a result, hybrid earthquake models based on both geodesy and seismicity are the most informative seismicity models during the testing time frame, as they obtain higher information scores than their constituent model components. These results support the combination of interseismic strain measurements with earthquake-catalog data for improved seismicity modeling. However, further prospective evaluations are required to more accurately describe the capacities of these global ensemble seismicity models to forecast longer-term earthquake activity.},
  language  = {en}
}
@phdthesis{Ibarra2021,
  author    = {Ibarra, Federico},
  title     = {The thermal and rheological state of the Central Andes and its relationship to active deformation processes},
  doi       = {10.25932/publishup-50622},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-506226},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 149},
  year      = {2021},
  abstract  = {The Central Andes region in South America is characterized by a complex and heterogeneous deformation system. Recorded seismic activity and mapped neotectonic structures indicate that most of the intraplate deformation is located along the margins of the orogen, in the transitions to the foreland and the forearc. Furthermore, the actively deforming provinces of the foreland exhibit distinct deformation styles that vary along strike, as well as characteristic distributions of seismicity with depth. The style of deformation transitions from thin-skinned in the north to thick-skinned in the south, and the thickness of the seismogenic layer increases to the south. Based on geological/geophysical observations and numerical modelling, the most commonly invoked causes for the observed heterogeneity are the variations in sediment thickness and composition, the presence of inherited structures, and changes in the dip of the subducting Nazca plate. However, there are still no comprehensive investigations on the relationship between the lithospheric composition of the Central Andes, its rheological state and the observed deformation processes. The central aim of this dissertation is therefore to explore the link between the nature of the lithosphere in the region and the location of active deformation. The study of the lithospheric composition by means of independent-data integration establishes a strong base to assess the thermal and rheological state of the Central Andes and its adjacent lowlands, which alternatively provide new foundations to understand the complex deformation of the region. In this line, the general workflow of the dissertation consists in the construction of a 3D data-derived and gravity-constrained density model of the Central Andean lithosphere, followed by the simulation of the steady-state conductive thermal field and the calculation of strength distribution. Additionally, the dynamic response of the orogen-foreland system to intraplate compression is evaluated by means of 3D geodynamic modelling. The results of the modelling approach suggest that the inherited heterogeneous composition of the lithosphere controls the present-day thermal and rheological state of the Central Andes, which in turn influence the location and depth of active deformation processes. Most of the seismic activity and neo--tectonic structures are spatially correlated to regions of modelled high strength gradients, in the transition from the felsic, hot and weak orogenic lithosphere to the more mafic, cooler and stronger lithosphere beneath the forearc and the foreland. Moreover, the results of the dynamic simulation show a strong localization of deviatoric strain rate second invariants in the same region suggesting that shortening is accommodated at the transition zones between weak and strong domains. The vertical distribution of seismic activity appears to be influenced by the rheological state of the lithosphere as well. The depth at which the frequency distribution of hypocenters starts to decrease in the different morphotectonic units correlates with the position of the modelled brittle-ductile transitions; accordingly, a fraction of the seismic activity is located within the ductile part of the crust. An exhaustive analysis shows that practically all the seismicity in the region is restricted above the 600°C isotherm, in coincidence with the upper temperature limit for brittle behavior of olivine. Therefore, the occurrence of earthquakes below the modelled brittle-ductile could be explained by the presence of strong residual mafic rocks from past tectonic events. Another potential cause of deep earthquakes is the existence of inherited shear zones in which brittle behavior is favored through a decrease in the friction coefficient. This hypothesis is particularly suitable for the broken foreland provinces of the Santa Barbara System and the Pampean Ranges, where geological studies indicate successive reactivation of structures through time. Particularly in the Santa Barbara System, the results indicate that both mafic rocks and a reduction in friction are required to account for the observed deep seismic events.},
  language  = {en}
}
@phdthesis{Duesing2021,
  author    = {D{\"u}sing, Walter},
  title     = {From changes in the Earth's orbit to African climate variability},
  doi       = {10.25932/publishup-50314},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-503140},
  school      = {Universit{\"a}t Potsdam},
  pages     = {77},
  year      = {2021},
  abstract  = {We developed an orbital tuned age model for the composite Chew Bahir sediment core, obtained from the Chew Bahir basin (CHB), southern Ethiopia. To account for the effects of sedimentation rate changes on the spectral expression of the orbital cycles we developed a new method: the Multi-band Wavelet Age modeling technique (MUBAWA). By using a Continuous Wavelet Transformation, we were able to track frequency shifts that resulted from changing sedimentation rates and thus calculated tuned age model encompassing the last 620 kyrs. The results show a good agreement with the directly dated age model that is available from the dating of volcanic ashes. Then we used the XRF data from CHB and developed a new and robust humid-arid index of east African climate during the last 620 kyrs. To disentangle the relationship of the selected elements we performed a principal component analysis (PCA). In a following step we applied a continuous wavelet transformation on the PC1, using the directly dated age model. The resulting wavelet power spectrum, unlike a normal power spectrum, displays the occurrence of cycles/frequencies in time. The results highlight that the precession cycles are most dominantly expressed under the 400 kyrs eccentricity maximum whereas weakly expressed during eccentricity minimum. This suggests that insolation is a key driver of the climatic variability observed at CHB throughout the last 620 kyrs. In addition, the prevalence of half-precession and obliquity signals was documented. The latter is attributed to the inter-tropical insolation gradient and not interpreted as an imprint of high latitudes forcing on climatic changes in the tropics. In addition, a windowed analysis of variability was used to detect changes in variance over time and showed that strong climate variability occurred especially along the transition from a dominant insolation-controlled humid climate background state towards a predominantly dry and less-insolation controlled climate. The last chapter dealt with non-linear aspects of climate changes represented by the sediments of the CHB. We use recurrence quantification analysis to detect non-linear changes within the potassium concentration of Chew Bahir sediment cores during the last 620 kyrs. The concentration of potassium in the sediments of the lake is subject to geochemical processes related to the evaporation rate of the lake water at the time of deposition. Based on recurrence analysis, two types of variabilities could be distinguished. Type 1 represents slow variations within the precession period bandwidth of 20 kyrs and a tendency towards extreme climatic events whereas type 2 represents fast, highly variable climatic transitions between wet and dry climate states. While type 1 variability is linked to eccentricity maxima, type 2 variability occurs during the 400 kyrs eccentricity minimum. The climate history presented here shows that during high eccentricity a strongly insolation-driven climate system prevailed, whereas during low eccentricity the climate was more strongly affected by short-term variability changes. The short-term environmental changes, reflected in the increased variability might have influenced the evolution, technological advances and expansion of early modern humans who lived in this region. In the Olorgesaille Basin the temporal changes in the occurrence of stone tools, which bracket the transition from Acheulean to Middle Stone Age (MSA) technologies at between 499-320 kyrs, could potentially correlate to the marked transition from a rather stable climate with less variability to a climate with increased variability in the CHB. We conclude that populations of early anatomically modern humans are more likely to have experienced climatic stress during episodes of low eccentricity, associated with dry and high variability climate conditions, which may have led to technological innovation, such as the transition from the Acheulean to the Middle Stone Age.},
  language  = {en}
}
@phdthesis{Angelopoulos2020,
  author    = {Angelopoulos, Michael},
  title     = {Mechanisms of sub-aquatic permafrost evolution in Arctic coastal environments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {165},
  year      = {2020},
  abstract  = {Subsea permafrost is perennially cryotic earth material that lies offshore. Most submarine permafrost is relict terrestrial permafrost beneath the Arctic shelf seas, was inundated after the last glaciation, and has been warming and thawing ever since. It is a reservoir and confining layer for gas hydrates and has the potential to release greenhouse gases and affect global climate change. Furthermore, subsea permafrost thaw destabilizes coastal infrastructure. While numerous studies focus on its distribution and rate of thaw over glacial timescales, these studies have not been brought together and examined in their entirety to assess rates of thaw beneath the Arctic Ocean. In addition, there is still a large gap in our understanding of sub-aquatic permafrost processes on finer spatial and temporal scales. The degradation rate of subsea permafrost is influenced by the initial conditions upon submergence. Terrestrial permafrost that has already undergone warming, partial thawing or loss of ground ice may react differently to inundation by seawater compared to previously undisturbed ice-rich permafrost. Heat conduction models are sufficient to model the thaw of thick subsea permafrost from the bottom, but few studies have included salt diffusion for top-down chemical degradation in shallow waters characterized by mean annual cryotic conditions on the seabed. Simulating salt transport is critical for assessing degradation rates for recently inundated permafrost, which may accelerate in response to warming shelf waters, a lengthening open water season, and faster coastal erosion rates. In the nearshore zone, degradation rates are also controlled by seasonal processes like bedfast ice, brine injection, seasonal freezing under floating ice conditions and warm freshwater discharge from large rivers. The interplay of all these variables is complex and needs further research. To fill this knowledge gap, this thesis investigates sub-aquatic permafrost along the southern coast of the Bykovsky Peninsula in eastern Siberia. Sediment cores and ground temperature profiles were collected at a freshwater thermokarst lake and two thermokarst lagoons in 2017. At this site, the coastline is retreating, and seawater is inundating various types of permafrost: sections of ice-rich Pleistocene permafrost (Yedoma) cliffs at the coastline alternate with lagoons and lower elevation previously thawed and refrozen permafrost basins (Alases). Electrical resistivity surveys with floating electrodes were carried out to map ice-bearing permafrost and taliks (unfrozen zones in the permafrost, usually formed beneath lakes) along the diverse coastline and in the lagoons. Combined with the borehole data, the electrical resistivity results permit estimation of contemporary ice-bearing permafrost characteristics, distribution, and occasionally, thickness. To conceptualize possible geomorphological and marine evolutionary pathways to the formation of the observed layering, numerical models were applied. The developed model incorporates salt diffusion and seasonal dynamics at the seabed, including bedfast ice. Even along coastlines with mean annual non-cryotic boundary conditions like the Bykovsky Peninsula, the modelling results show that salt diffusion minimizes seasonal freezing of the seabed, leading to faster degradation rates compared to models without salt diffusion. Seasonal processes are also important for thermokarst lake to lagoon transitions because lagoons can generate cold hypersaline conditions underneath the ice cover. My research suggests that ice-bearing permafrost can form in a coastal lagoon environment, even under floating ice. Alas basins, however, may degrade more than twice as fast as Yedoma permafrost in the first several decades of inundation. In addition to a lower ice content compared to Yedoma permafrost, Alas basins may be pre-conditioned with salt from adjacent lagoons. Considering the widespread distribution of thermokarst in the Arctic, its integration into geophysical models and offshore surveys is important to quantify and understand subsea permafrost degradation and aggradation. Through numerical modelling, fieldwork, and a circum-Arctic review of subsea permafrost literature, this thesis provides new insights into sub-aquatic permafrost evolution in saline coastal environments.},
  language  = {en}
}
@phdthesis{MogrovejoArias2021,
  author    = {Mogrovejo Arias, Diana Carolina},
  title     = {Assessment of the frequency and relevance of potentially pathogenic phenotypes in microbial isolates from Arctic environments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {125},
  year      = {2021},
  abstract  = {The Arctic environments constitute rich and dynamic ecosystems, dominated by microorganisms extremely well adapted to survive and function under severe conditions. A range of physiological adaptations allow the microbiota in these habitats to withstand low temperatures, low water and nutrient availability, high levels of UV radiation, etc. In addition, other adaptations of clear competitive nature are directed at not only surviving but thriving in these environments, by disrupting the metabolism of neighboring cells and affecting intermicrobial communication. Since Arctic microbes are bioindicators which amplify climate alterations in the environment, the Arctic region presents the opportunity to study local microbiota and carry out research about interesting, potentially virulent phenotypes that could be dispersed into other habitats around the globe as a consequence of accelerating climate change. In this context, exploration of Arctic habitats as well as descriptions of the microbes inhabiting them are abundant but microbial competitive strategies commonly associated with virulence and pathogens are rarely reported. In this project, environmental samples from the Arctic region were collected and microorganisms (bacteria and fungi) were isolated. The clinical relevance of these microorganisms was assessed by observing the following virulence markers: ability to grow at a range of temperatures, expression of antimicrobial resistance and production of hemolysins. The aim of this project is to determine the frequency and relevance of these characteristics in an effort to understand microbial adaptations in habitats threatened by climate change. The isolates obtained and described here were able to grow at a range of temperatures, in some cases more than 30 °C higher than their original isolation temperature. A considerable number of them consistently expressed compounds capable of lysing sheep and bovine erythrocytes on blood agar at different incubation temperatures. Ethanolic extracts of these bacteria were able to cause rapid and complete lysis of erythrocyte suspensions and might even be hemolytic when assayed on human blood. In silico analyses showed a variety of resistance elements, some of them novel, against natural and synthetic antimicrobial compounds. In vitro experiments against a number of antimicrobial compounds showed resistance phenotypes belonging to wild-type populations and some non-wild type which clearly denote human influence in the acquisition of antimicrobial resistance. The results of this project demonstrate the presence of virulence-associated factors expressed by microorganisms of natural, non-clinical environments. This study contains some of the first reports, to the best of our knowledge, of hemolytic microbes isolated from the Arctic region. In addition, it provides additional information about the presence and expression of intrinsic and acquired antimicrobial resistance in environmental isolates, contributing to the understanding of the evolution of relevant pathogenic species and opportunistic pathogens. Finally, this study highlights some of the potential risks associated with changes in the polar regions (habitat melting and destruction, ecosystem transition and re-colonization) as important indirect consequences of global warming and altered climatic conditions around the planet.},
  language  = {en}
}
@phdthesis{Koerting2021,
  author    = {Koerting, Friederike Magdalena},
  title     = {Hybrid imaging spectroscopy approaches for open pit mining},
  doi       = {10.25932/publishup-49909},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-499091},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxix, 269},
  year      = {2021},
  abstract  = {This work develops hybrid methods of imaging spectroscopy for open pit mining and examines their feasibility compared with state-of-the-art. The material distribution within a mine face differs in the small scale and within daily assigned extraction segments. These changes can be relevant to subsequent processing steps but are not always visually identifiable prior to the extraction. Misclassifications that cause false allocations of extracted material need to be minimized in order to reduce energy-intensive material re-handling. The use of imaging spectroscopy aspires to the allocation of relevant deposit-specific materials before extraction, and allows for efficient material handling after extraction. The aim of this work is the parameterization of imaging spectroscopy for pit mining applications and the development and evaluation of a workflow for a mine face, ground- based, spectral characterization. In this work, an application-based sensor adaptation is proposed. The sensor complexity is reduced by down-sampling the spectral resolution of the system based on the samples' spectral characteristics. This was achieved by the evaluation of existing hyperspectral outcrop analysis approaches based on laboratory sample scans from the iron quadrangle in Minas Gerais, Brazil and by the development of a spectral mine face monitoring workflow which was tested for both an operating and an inactive open pit copper mine in the Republic of Cyprus. The workflow presented here is applied to three regional data sets: 1) Iron ore samples from Brazil, (laboratory); 2) Samples and hyperspectral mine face imagery from the copper-gold-pyrite mine Apliki, Republic of Cyprus (laboratory and mine face data); and 3) Samples and hyperspectral mine face imagery from the copper-gold-pyrite deposit Three Hills, Republic of Cyprus (laboratory and mine face data). The hyperspectral laboratory dataset of fifteen Brazilian iron ore samples was used to evaluate different analysis methods and different sensor models. Nineteen commonly used methods to analyze and map hyperspectral data were compared regarding the methods' resulting data products and the accuracy of the mapping and the analysis computation time. Four of the evaluated methods were determined for subsequent analyses to determine the best-performing algorithms: The spectral angle mapper (SAM), a support vector machine algorithm (SVM), the binary feature fitting algorithm (BFF) and the EnMap geological mapper (EnGeoMap). Next, commercially available imaging spectroscopy sensors were evaluated for their usability in open pit mining conditions. Step-wise downsampling of the data - the reduction of the number of bands with an increase of each band's bandwidth - was performed to investigate the possible simplification and ruggedization of a sensor without a quality fall-off of the mapping results. The impact of the atmosphere visible in the spectrum between 1300-2010nm was reduced by excluding the spectral range from the data for mapping. This tested the feasibility of the method under realistic open pit data conditions. Thirteen datasets based on the different, downsampled sensors were analyzed with the four predetermined methods. The optimum sensor for spectral mine face material distinction was determined as a VNIR-SWIR sensor with 40nm bandwidths in the VNIR and 15nm bandwidths in the SWIR spectral range and excluding the atmospherically impacted bands. The Apliki mine sample dataset was used for the application of the found optimal analyses and sensors. Thirty-six samples were analyzed geochemically and mineralogically. The sample spectra were compiled to two spectral libraries, both distinguishing between seven different geochemical-spectral clusters. The reflectance dataset was downsampled to five different sensors. The five different datasets were mapped with the SAM, BFF and SVM method achieving mapping accuracies of 85-72\%, 85-76\% and 57-46\% respectively. One mine face scan of Apliki was used for the application of the developed workflow. The mapping results were validated against the geochemistry and mineralogy of thirty-six documented field sampling points and a zonation map of the mine face which is based on sixty-six samples and field mapping. The mine face was analyzed with SAM and BFF. The analysis maps were visualized on top of a Structure-from-Motion derived 3D model of the open pit. The mapped geological units and zones correlate well with the expected zonation of the mine face. The third set of hyperspectral imagery from Three Hills was available for applying the fully-developed workflow. Geochemical sample analyses and laboratory spectral data of fifteen different samples from the Three Hills mine, Republic of Cyprus, were used to analyse a downsampled mine face scan of the open pit. Here, areas of low, medium and high ore content were identified. The developed workflow is successfully applied to the open pit mines Apliki and Three Hills and the spectral maps reflect the prevailing geological conditions. This work leads through the acquisition, preparation and processing of imaging spectroscopy data, the optimum choice of analysis methodology, and the utilization of simplified, robust sensors that meet the requirements of open pit mining conditions. It accentuates the importance of a site-specific and deposit-specific spectral library for the mine face analysis and underlines the need for geological and spectral analysis experts to successfully implement imaging spectroscopy in the field of open pit mining.},
  language  = {en}
}
@phdthesis{Repasch2021,
  author    = {Repasch, Marisa},
  title     = {Fluvial sediment routing and the carbon cycle},
  doi       = {10.25932/publishup-49397},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-493978},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 176},
  year      = {2021},
  abstract  = {By regulating the concentration of carbon in our atmosphere, the global carbon cycle drives changes in our planet's climate and habitability. Earth surface processes play a central, yet insufficiently constrained role in regulating fluxes of carbon between terrestrial reservoirs and the atmosphere. River systems drive global biogeochemical cycles by redistributing significant masses of carbon across the landscape. During fluvial transit, the balance between carbon oxidation and preservation determines whether this mass redistribution is a net atmospheric CO2 source or sink. Existing models for fluvial carbon transport fail to integrate the effects of sediment routing processes, resulting in large uncertainties in fluvial carbon fluxes to the oceans. In this Ph.D. dissertation, I address this knowledge gap through three studies that focus on the timescale and routing pathways of fluvial mass transfer and show their effect on the composition and fluxes of organic carbon exported by rivers. The hypotheses posed in these three studies were tested in an analog lowland alluvial river system - the Rio Bermejo in Argentina. The Rio Bermejo annually exports more than 100 Mt of sediment and organic matter from the central Andes, and transports this material nearly 1300 km downstream across the lowland basin without influence from tributaries, allowing me to isolate the effects of geomorphic processes on fluvial organic carbon cycling. These studies focus primarily on the geochemical composition of suspended sediment collected from river depth profiles along the length of the Rio Bermejo. In Chapter 3, I aimed to determine the mean fluvial sediment transit time for the Rio Bermejo and evaluate the geomorphic processes that regulate the rate of downstream sediment transfer. I developed a framework to use meteoric cosmogenic 10Be (10Bem) as a chronometer to track the duration of sediment transit from the mountain front downstream along the ~1300 km channel of the Rio Bermejo. I measured 10Bem concentrations in suspended sediment sampled from depth profiles, and found a 230\% increase along the fluvial transit pathway. I applied a simple model for the time-dependent accumulation of 10Bem on the floodplain to estimate a mean sediment transit time of 8.5±2.2 kyr. Furthermore, I show that sediment transit velocity is influenced by lateral migration rate and channel morphodynamics. This approach to measuring sediment transit time is much more precise than other methods previously used and shows promise for future applications. In Chapter 4, I aimed to quantify the effects of hydrodynamic sorting on the composition and quantity of particulate organic carbon (POC) export transported by lowland rivers. I first used scanning electron miscroscopy (SEM) coupled with nanoscale secondary ion mass spectrometry (NanoSIMS) analyses to show that the Bermejo transports two principal types of POC: 1) mineral-bound organic carbon associated with <4 µm, platy grains, and 2) coarse discrete organic particles. Using n-alkane stable isotope data and particle shape analysis, I showed that these two carbon pools are vertically sorted in the water column, due to differences in particle settling velocity. This vertical sorting may drive modern POC to be transported efficiently from source-to-sink, driving efficient CO2 drawdown. Simultaneously, vertical sorting may drive degraded, mineral-bound POC to be deposited overbank and stored on the floodplain for centuries to millennia, resulting in enhanced POC remineralization. In the Rio Bermejo, selective deposition of coarse material causes the proportion of mineral-bound POC to increase with distance downstream, but the majority of exported POC is composed of discrete organic particles, suggesting that the river is a net carbon sink. In summary, this study shows that selective deposition and hydraulic sorting control the composition and fate of fluvial POC during fluvial transit. In Chapter 5, I characterized and quantified POC transformation and oxidation during fluvial transit. I analyzed the radiocarbon content and stable carbon isotopic composition of Rio Bermejo suspended sediment and found that POC ages during fluvial transit, but is also degraded and oxidized during transient floodplain storage. Using these data, I developed a conceptual model for fluvial POC cycling that allows the estimation of POC oxidation relative to POC export, and ultimately reveals whether a river is a net source or sink of CO2 to the atmosphere. Through this study, I found that the Rio Bermejo annually exports more POC than is oxidized during transit, largely due to high rates of lateral migration that cause erosion of floodplain vegetation and soil into the river. These results imply that human engineering of rivers could alter the fluvial carbon balance, by reducing lateral POC inputs and increasing the mean sediment transit time. Together, these three studies quantitatively link geomorphic processes to rates of POC transport and degradation across sub-annual to millennial time scales and nanoscale to 103 km spatial scales, laying the groundwork for a global-scale fluvial organic carbon cycling model.},
  language  = {en}
}
@phdthesis{TabaresJimenez2021,
  author    = {Tabares Jimenez, Ximena del Carmen},
  title     = {A palaeoecological approach to savanna dynamics and shrub encroachment in Namibia},
  doi       = {10.25932/publishup-49281},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-492815},
  school      = {Universit{\"a}t Potsdam},
  pages     = {121},
  year      = {2021},
  abstract  = {The spread of shrubs in Namibian savannas raises questions about the resilience of these ecosystems to global change. This makes it necessary to understand the past dynamics of the vegetation, since there is no consensus on whether shrub encroachment is a new phenomenon, nor on its main drivers. However, a lack of long-term vegetation datasets for the region and the scarcity of suitable palaeoecological archives, makes reconstructing past vegetation and land cover of the savannas a challenge. To help meet this challenge, this study addresses three main research questions: 1) is pollen analysis a suitable tool to reflect the vegetation change associated with shrub encroachment in savanna environments? 2) Does the current encroached landscape correspond to an alternative stable state of savanna vegetation? 3) To what extent do pollen-based quantitative vegetation reconstructions reflect changes in past land cover? The research focuses on north-central Namibia, where despite being the region most affected by shrub invasion, particularly since the 21st century, little is known about the dynamics of this phenomenon. Field-based vegetation data were compared with modern pollen data to assess their correspondence in terms of composition and diversity along precipitation and grazing intensity gradients. In addition, two sediment cores from Lake Otjikoto were analysed to reveal changes in vegetation composition that have occurred in the region over the past 170 years and their possible drivers. For this, a multiproxy approach (fossil pollen, sedimentary ancient DNA (sedaDNA), biomarkers, compound specific carbon (δ13C) and deuterium (δD) isotopes, bulk carbon isotopes (δ13Corg), grain size, geochemical properties) was applied at high taxonomic and temporal resolution. REVEALS modelling of the fossil pollen record from Lake Otjikoto was run to quantitatively reconstruct past vegetation cover. For this, we first made pollen productivity estimates (PPE) of the most relevant savanna taxa in the region using the extended R-value model and two pollen dispersal options (Gaussian plume model and Lagrangian stochastic model). The REVEALS-based vegetation reconstruction was then validated using remote sensing-based regional vegetation data. The results show that modern pollen reflects the composition of the vegetation well, but diversity less well. Interestingly, precipitation and grazing explain a significant amount of the compositional change in the pollen and vegetation spectra. The multiproxy record shows that a state change from open Combretum woodland to encroached Terminalia shrubland can occur over a century, and that the transition between states spans around 80 years and is characterized by a unique vegetation composition. This transition is supported by gradual environmental changes induced by management (i.e. broad-scale logging for the mining industry, selective grazing and reduced fire activity associated with intensified farming) and related land-use change. Derived environmental changes (i.e. reduced soil moisture, reduced grass cover, changes in species composition and competitiveness, reduced fire intensity) may have affected the resilience of Combretum open woodlands, making them more susceptible to change to an encroached state by stochastic events such as consecutive years of precipitation and drought, and by high concentrations of pCO2. We assume that the resulting encroached state was further stabilized by feedback mechanisms that favour the establishment and competitiveness of woody vegetation. The REVEALS-based quantitative estimates of plant taxa indicate the predominance of a semi-open landscape throughout the 20th century and a reduction in grass cover below 50\% since the 21st century associated with the spread of encroacher woody taxa. Cover estimates show a close match with regional vegetation data, providing support for the vegetation dynamics inferred from multiproxy analyses. Reasonable PPEs were made for all woody taxa, but not for Poaceae. In conclusion, pollen analysis is a suitable tool to reconstruct past vegetation dynamics in savannas. However, because pollen cannot identify grasses beyond family level, a multiproxy approach, particularly the use of sedaDNA, is required. I was able to separate stable encroached states from mere woodland phases, and could identify drivers and speculate about related feedbacks. In addition, the REVEALS-based quantitative vegetation reconstruction clearly reflects the magnitude of the changes in the vegetation cover that occurred during the last 130 years, despite the limitations of some PPEs. This research provides new insights into pollen-vegetation relationships in savannas and highlights the importance of multiproxy approaches when reconstructing past vegetation dynamics in semi-arid environments. It also provides the first time series with sufficient taxonomic resolution to show changes in vegetation composition during shrub encroachment, as well as the first quantitative reconstruction of past land cover in the region. These results help to identify the different stages in savanna dynamics and can be used to calibrate predictive models of vegetation change, which are highly relevant to land management.},
  language  = {en}
}
@phdthesis{Holm2020,
  author    = {Holm, Stine},
  title     = {Methanogenic communities and metaplasmidome-encoded functions in permafrost environments exposed to thaw},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 243},
  year      = {2020},
  abstract  = {This thesis investigates how the permafrost microbiota responds to global warming. In detail, the constraints behind methane production in thawing permafrost were linked to methanogenic activity, abundance and composition. Furthermore, this thesis offers new insights into microbial adaptions to the changing environmental conditions during global warming. This was assesed by investigating the potential ecological relevant functions encoded by plasmid DNA within the permafrost microbiota. Permafrost of both interglacial and glacial origin spanning the Holocene to the late Pleistocene, including Eemian, were studied during long-term thaw incubations. Furthermore, several permafrost cores of different stratigraphy, soil type and vegetation cover were used to target the main constraints behind methane production during short-term thaw simulations. Short- and long-term incubations simulating thaw with and without the addition of substrate were combined with activity measurements, amplicon and metagenomic sequencing of permanently frozen and seasonally thawed active layer. Combined, it allowed to address the following questions. i) What constraints methane production when permafrost thaws and how is this linked to methanogenic activity, abundance and composition? ii) How does the methanogenic community composition change during long-term thawing conditions? iii) Which potential ecological relevant functions are encoded by plasmid DNA in active layer soils? The major outcomes of this thesis are as follows. i) Methane production from permafrost after long-term thaw simulation was found to be constrained mainly by the abundance of methanogens and the archaeal community composition. Deposits formed during periods of warmer temperatures and increased precipitation, (here represented by deposits from the Late Pleistocene of both interstadial and interglacial periods) were found to respond strongest to thawing conditions and to contain an archaeal community dominated by methanogenic archaea (40\% and 100\% of all detected archaea). Methanogenic population size and carbon density were identified as main predictors for potential methane production in thawing permafrost in short-term incubations when substrate was sufficiently available. ii) Besides determining the methanogenic activity after long-term thaw, the paleoenvironmental conditions were also found to influence the response of the methanogenic community composition. Substantial shifts within methanogenic community structure and a drop in diversity were observed in deposits formed during warmer periods, but not in deposits from stadials, when colder and drier conditions occurred. Overall, a shift towards a dominance of hydrogenotrophic methanogens was observed in all samples, except for the oldest interglacial deposits from the Eemian, which displayed a potential dominance of acetoclastic methanogens. The Eemian, which is discussed to serve as an analogue to current climate conditions, contained highly active methanogenic communities. However, all potential limitation of methane production after permafrost thaw, it means methanogenic community structure, methanogenic population size, and substrate pool might be overcome after permafrost had thawed on the long-term. iii) Enrichments with soil from the seasonally thawed active layer revealed that its plasmid DNA ('metaplasmidome') carries stress-response genes. In particular it encoded antibiotic resistance genes, heavy metal resistance genes, cold shock proteins and genes encoding UV-protection. Those are functions that are directly involved in the adaptation of microbial communities to stresses in polar environments. It was further found that metaplasmidomes from the Siberian active layer originate mainly from Gammaproteobacteria. By applying enrichment cultures followed by plasmid DNA extraction it was possible to obtain a higher average contigs length and significantly higher recovery of plasmid sequences than from extracting plasmid sequences from metagenomes. The approach of analyzing 'metaplasmidomes' established in this thesis is therefore suitable for studying the ecological role of plasmids in polar environments in general. This thesis emphasizes that including microbial community dynamics have the potential to improve permafrost-carbon projections. Microbially mediated methane release from permafrost environments may significantly impact future climate change. This thesis identified drivers of methanogenic composition, abundance and activity in thawing permafrost landscapes. Finally, this thesis underlines the importance to study how the current warming Arctic affects microbial communities in order to gain more insight into microbial response and adaptation strategies.},
  language  = {en}
}
@phdthesis{Meijer2020,
  author    = {Meijer, Niels},
  title     = {Asian dust, monsoons and westerlies during the Eocene},
  doi       = {10.25932/publishup-48868},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-488687},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 155},
  year      = {2020},
  abstract  = {The East Asian monsoons characterize the modern-day Asian climate, yet their geological history and driving mechanisms remain controversial. The southeasterly summer monsoon provides moisture, whereas the northwesterly winter monsoon sweeps up dust from the arid Asian interior to form the Chinese Loess Plateau. The onset of this loess accumulation, and therefore of the monsoons, was thought to be 8 million years ago (Ma). However, in recent years these loess records have been extended further back in time to the Eocene (56-34 Ma), a period characterized by significant changes in both the regional geography and global climate. Yet the extent to which these reconfigurations drive atmospheric circulation and whether the loess-like deposits are monsoonal remains debated. In this thesis, I study the terrestrial deposits of the Xining Basin previously identified as Eocene loess, to derive the paleoenvironmental evolution of the region and identify the geological processes that have shaped the Asian climate. I review dust deposits in the geological record and conclude that these are commonly represented by a mix of both windblown and water-laid sediments, in contrast to the pure windblown material known as loess. Yet by using a combination of quartz surface morphologies, provenance characteristics and distinguishing grain-size distributions, windblown dust can be identified and quantified in a variety of settings. This has important implications for tracking aridification and dust-fluxes throughout the geological record. Past reversals of Earth's magnetic field are recorded in the deposits of the Xining Basin and I use these together with a dated volcanic ash layer to accurately constrain the age to the Eocene period. A combination of pollen assemblages, low dust abundances and other geochemical data indicates that the early Eocene was relatively humid suggesting an intensified summer monsoon due to the warmer greenhouse climate at this time. A subsequent shift from predominantly freshwater to salt lakes reflects a long-term aridification trend possibly driven by global cooling and the continuous uplift of the Tibetan Plateau. Superimposed on this aridification are wetter intervals reflected in more abundant lake deposits which correlate with highstands of the inland proto-Paratethys Sea. This sea covered the Eurasian continent and thereby provided additional moisture to the winter-time westerlies during the middle to late Eocene. The long-term aridification culminated in an abrupt shift at 40 Ma reflected by the onset of windblown dust, an increase in steppe-desert pollen, the occurrence of high-latitude orbital cycles and northwesterly winds identified in deflated salt deposits. Together, these indicate the onset of a Siberian high atmospheric pressure system driving the East Asian winter monsoon as well as dust storms and was triggered by a major sea retreat from the Asian interior. These results therefore show that the proto-Paratethys Sea, though less well recognized than the Tibetan Plateau and global climate, has been a major driver in setting up the modern-day climate in Asia.},
  language  = {en}
}
@phdthesis{Wang2020,
  author    = {Wang, Xia},
  title     = {Reef ecosystem recovery following the Middle Permian (Capitanian) mass extinction},
  doi       = {10.25932/publishup-48750},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-487502},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XI, 144},
  year      = {2020},
  abstract  = {To find out the future of nowadays reef ecosystem turnover under the environmental stresses such as global warming and ocean acidification, analogue studies from the geologic past are needed. As a critical time of reef ecosystem innovation, the Permian-Triassic transition witnessed the most severe demise of Phanerozoic reef builders, and the establishment of modern style symbiotic relationships within the reef-building organisms. Being the initial stage of this transition, the Middle Permian (Capitanian) mass extinction coursed a reef eclipse in the early Late Permian, which lead to a gap of understanding in the post-extinction Wuchiapingian reef ecosystem, shortly before the radiation of Changhsingian reefs. Here, this thesis presents detailed biostratigraphic, sedimentological, and palaeoecological studies of the Wuchiapingian reef recovery following the Middle Permian (Capitanian) mass extinction, on the only recorded Wuchiapingian reef setting, outcropping in South China at the Tieqiao section. Conodont biostratigraphic zonations were revised from the Early Permian Artinskian to the Late Permian Wuchiapingian in the Tieqiao section. Twenty main and seven subordinate conodont zones are determined at Tieqiao section including two conodont zone below and above the Tieqiao reef complex. The age of Tieqiao reef was constrained as early to middle Wuchiapingian. After constraining the reef age, detailed two-dimensional outcrop mapping combined with lithofacies study were carried out on the Wuchiapingian Tieqiao Section to investigate the reef growth pattern stratigraphically as well as the lateral changes of reef geometry on the outcrop scale. Semi-quantitative studies of the reef-building organisms were used to find out their evolution pattern within the reef recovery. Six reef growth cycles were determined within six transgressive-regressive cycles in the Tieqiao section. The reefs developed within the upper part of each regressive phase and were dominated by different biotas. The timing of initial reef recovery after the Middle Permian (Capitanian) mass extinction was updated to the Clarkina leveni conodont zone, which is earlier than previous understanding. Metazoans such as sponges were not the major components of the Wuchiapingian reefs until the 5th and 6th cycles. So, the recovery of metazoan reef ecosystem after the Middle Permian (Capitanian) mass extinction was obviously delayed. In addition, although the importance of metazoan reef builders such as sponges did increase following the recovery process, encrusting organisms such as Archaeolithoporella and Tubiphytes, combined with microbial carbonate precipitation, still played significant roles to the reef building process and reef recovery after the mass extinction. Based on the results from outcrop mapping and sedimentological studies, quantitative composition analysis of the Tieqiao reef complex were applied on selected thin sections to further investigate the functioning of reef building components and the reef evolution after the Middle Permian (Capitanian) mass extinction. Data sets of skeletal grains and whole rock components were analyzed. The results show eleven biocommunity clusters/eight rock composition clusters dominated by different skeletal grains/rock components. Sponges, Archaeolithoporella and Tubiphytes were the most ecologically important components within the Wuchiapingian Tieqiao reef, while the clotted micrites and syndepositional cements are the additional important rock components for reef cores. The sponges were important within the whole reef recovery. Tubiphytes were broadly distributed in different environments and played a key-role in the initial reef communities. Archaeolithoporella concentrated in the shallower part of reef cycles (i.e., the upper part of reef core) and was functionally significant for the enlargement of reef volume. In general, the reef recovery after the Middle Permian (Capitanian) mass extinction has some similarities with the reef recovery following the end-Permian mass extinction. It shows a delayed recovery of metazoan reefs and a stepwise recovery pattern that was controlled by both ecological and environmental factors. The importance of encrusting organisms and microbial carbonates are also similar to most of the other post-extinction reef ecosystems. These findings can be instructive to extend our understanding of the reef ecosystem evolution under environmental perturbation or stresses.},
  language  = {en}
}
@phdthesis{Zorn2020,
  author    = {Zorn, Edgar Ulrich},
  title     = {Monitoring lava dome growth and deformation with photogrammetric methods and modelling},
  doi       = {10.25932/publishup-48360},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483600},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IX, 167},
  year      = {2020},
  abstract  = {Lava domes are severely hazardous, mound-shaped extrusions of highly viscous lava and commonly erupt at many active stratovolcanoes around the world. Due to gradual growth and flank oversteepening, such lava domes regularly experience partial or full collapses, resulting in destructive and far-reaching pyroclastic density currents. They are also associated with cyclic explosive activity as the complex interplay of cooling, degassing, and solidification of dome lavas regularly causes gas pressurizations on the dome or the underlying volcano conduit. Lava dome extrusions can last from days to decades, further highlighting the need for accurate and reliable monitoring data. This thesis aims to improve our understanding of lava dome processes and to contribute to the monitoring and prediction of hazards posed by these domes. The recent rise and sophistication of photogrammetric techniques allows for the extraction of observational data in unprecedented detail and creates ideal tools for accomplishing this purpose. Here, I study natural lava dome extrusions as well as laboratory-based analogue models of lava dome extrusions and employ photogrammetric monitoring by Structure-from-Motion (SfM) and Particle-Image-Velocimetry (PIV) techniques. I primarily use aerial photography data obtained by helicopter, airplanes, Unoccupied Aircraft Systems (UAS) or ground-based timelapse cameras. Firstly, by combining a long time-series of overflight data at Volc{\´a}n de Colima, M{\´e}xico, with seismic and satellite radar data, I construct a detailed timeline of lava dome and crater evolution. Using numerical model, the impact of the extrusion on dome morphology and loading stress is further evaluated and an impact on the growth direction is identified, bearing important implications for the location of collapse hazards. Secondly, sequential overflight surveys at the Santiaguito lava dome, Guatemala, reveal surface motion data in high detail. I quantify the growth of the lava dome and the movement of a lava flow, showing complex motions that occur on different timescales and I provide insight into rock properties relevant for hazard assessment inferred purely by photogrammetric processing of remote sensing data. Lastly, I recreate artificial lava dome and spine growth using analogue modelling under controlled conditions, providing new insights into lava extrusion processes and structures as well as the conditions in which they form. These findings demonstrate the capabilities of photogrammetric data analyses to successfully monitor lava dome growth and evolution while highlighting the advantages of complementary modelling methods to explain the observed phenomena. The results presented herein further bear important new insights and implications for the hazards posed by lava domes.},
  language  = {en}
}
@phdthesis{Kaya2020,
  author    = {Kaya, Mustafa},
  title     = {Cretaceous-Paleogene evolution of the proto-Paratethys Sea in Central Asia},
  doi       = {10.25932/publishup-48329},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483295},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 237},
  year      = {2020},
  abstract  = {Unlike today's prevailing terrestrial features, the geologic past of Central Asia witnessed marine environments and conditions as well. A vast, shallow sea, known as proto-Paratethys, extended across Eurasia from the Mediterranean Tethys to the Tarim Basin in western China during Cretaceous to Paleogene times. This sea formed about 160 million years ago (during Jurassic times) when the waters of the Tethys Ocean flooded into Eurasia. It drastically retreated to the west and became isolated as the Paratethys during the Late Eocene-Oligocene (ca. 34 Ma). Having well-constrained timing and paleogeography for the Cretaceous-Paleogene proto-Paratethys sea incursions in Central Asia is essential to properly understand and distinguish the controlling mechanisms and their link to Asian paleoenvironmental and paleoclimatic change. The Cretaceous-Paleogene tectonic evolution of the Pamir and Tibet and their far-field effects play a significant role on the sedimentological and structural evolution of the Central Asian basins and on the evolution of the proto-Paratethys sea fluctuations as well. Comparing the records of the sea incursions to the tectonic and eustatic events has paramount importance to reveal the controlling mechanisms behind the sea incursions. However, due to inaccuracies in the dating of rocks (mostly continental rocks and marine rocks with benthic microfossils providing low-resolution biostratigraphic constraints) and conflicting results, there has been no consensus on the timing of the sea incursions and interpretation of their records has been in question. Here, we present a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy as well as a detailed paleoenvironmental analysis for the Cretaceous and Paleogene proto-Paratethys Sea incursions in the Tajik and Tarim basins, in Central Asia. This enables us to identify the major drivers of marine fluctuations and their potential consequences on regional and global climate, particularly Asian aridification and the global carbon cycle perturbations such as the Paleocene-Eocene Thermal Maximum (PETM). To estimate the paleogeographic evolution of the proto-Paratethys Sea, the refined age constraints and detailed paleoenvironmental interpretations are combined with successive paleogeographic maps. Regional coastlines and depositional environments during the Cretaceous-Paleogene sea advances and retreats were drawn based on the results of this thesis and integrated with existing literature to generate new paleogeographic maps. Before its final westward retreat in the Eocene, a total of six Cretaceous and Paleogene major sea incursions have been distinguished from the sedimentary records of the Tajik and Tarim basins in Central Asia. All have been studied and documented here. We identify the presence of marine conditions already in the Early Cretaceous in the western Tajik Basin, followed by the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) major marine incursions far into the eastern Tajik and Tarim basins separated by a Turonian-Coniacian (ca. 92-86 Ma) regression. Basin-wide tectonic subsidence analyses imply that the Early Cretaceous invasion of the sea into the Tajik Basin is related to increased Pamir tectonism (at ca. 130 - 90 Ma) in a retro-arc basin setting inferred to be linked to collision and subduction. This tectonic event mainly governed the Cenomanian (ca. 100 Ma) sea incursion in conjunction with a coeval global eustatic high resulting in the maximum geographic extent of the sea. The following Turonian-Coniacian (ca. 92-86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence related to a regime change in Pamir tectonism from compression to extension. The Santonian (ca. 86 Ma) major sea incursion was more likely controlled dominantly by eustasy as also evidenced by the coeval fluctuations in the west Siberian Basin. During the early Maastrichtian, the global Late Cretaceous cooling is inferred from the disappearance of mollusk-rich limestones and the dominance of bryozoan-rich and echinoderm-rich limestones in the Tajik Basin documenting the first evidence for the Late Cretaceous cooling event in Central Asia. Following the last Cretaceous sea incursion, a major regional restriction event, marked by the exceptionally thick (≤ 400 m) shelf evaporites is assigned a Danian-Selandian age (ca. 63-59 Ma). This is followed by the largest recorded proto-Paratethys sea incursion with a transgression estimated as early Thanetian (ca. 59-57 Ma) and a regression within the Ypresian (ca. 53-52 Ma). The transgression of the next incursion is now constrained as early Lutetian (ca. 47-46 Ma), whereas its regression is constrained as late Lutetian (ca. 41 Ma) and is associated with a drastic increase in both tectonic subsidence and basin infilling. The age of the final and least pronounced sea incursion restricted to the westernmost margin of the Tarim Basin is assigned as Bartonian-Priabonian (ca. 39.7-36.7 Ma). We interpret the long-term westward retreat of the proto-Paratethys Sea starting at ca. 41 Ma to be associated with far-field tectonic effects of the Indo-Asia collision and Pamir/Tibetan plateau uplift. Short-term eustatic sea level transgressions are superimposed on this long-term regression and seem coeval with the transgression events in the other northern Peri-Tethyan sedimentary provinces for the 1st and 2nd Paleogene sea incursions. However, the last Paleogene sea incursion is interpreted as related to tectonism. The transgressive and regressive intervals of the proto-Paratethys Sea correlate well with the reported humid and arid phases, respectively in the Qaidam and Xining basins, thus demonstrating the role of the proto-Paratethys Sea as an important moisture source for the Asian interior and its regression as a contributor to Asian aridification. We lastly study the mechanics, relative contribution and preservation efficiency of ancient epicontinental seas as carbon sinks with new and existing data, using organic rich (sapropel) deposits dated to the PETM from the extensive epicontinental proto-Paratethys and West Siberian seas. We estimate ca. 1390±230 Gt organic C burial, a substantial amount compared to previously estimated global total excess organic C burial (ca. 1700-2900 Gt) is focused in the proto-Paratethys and West Siberian seas alone. We also speculate that enhanced organic carbon burial later over much of the proto-Paratethys (and later Paratethys) basin (during the deposition of the Kuma Formation and Maikop series, repectively) may have majorly contributed to drawdown of atmospheric carbon dioxide before and during the EOT cooling and glaciation of Antarctica. For past periods with smaller epicontinental seas, the effectiveness of this negative carbon cycle feedback was arguably diminished, and the same likely applies to the present-day.},
  language  = {en}
}
@phdthesis{Biedermann2020,
  author    = {Biedermann, Nicole},
  title     = {Carbonate-silicate reactions at conditions of the Earth's mantle and the role of carbonates as possible trace-element carriers},
  doi       = {10.25932/publishup-48277},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-482772},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 127},
  year      = {2020},
  abstract  = {Carbonates play a key role in the chemistry and dynamics of our planet. They are directly connected to the CO2 budget of our atmosphere and have a great impact on the deep carbon cycle. Moreover, recent studies have shown that carbonates are stable along the geothermal gradient down to Earth's lower mantle conditions, changing their crystal structure and related properties. Subducted carbonates may also react with silicates to form new phases. These reactions will redistribute elements, such as calcium (Ca), magnesium (Mg), iron (Fe) and carbon in the form of carbon dioxide (CO2), but also trace elements, that are carried by the carbonates. The trace elements of most interest are strontium (Sr) and rare earth elements (REE) which have been found to be important constituents in the composition of the primitive lower mantle and in mineral inclusions found in super-deep diamonds. However, the stability of carbonates in presence of mantle silicates at relevant temperatures is far from being well understood. Related to this, very little is known about distribution processes of trace elements between carbonates and mantle silicates. To shed light on these processes, we studied reactions between Sr- and REE-containing CaCO3 and Mg/Fe-bearing silicates of the system (Mg,Fe)2SiO4 - (Mg,Fe)SiO3 at high pressure and high temperature using synchrotron radiation based μ-X-ray diffraction (μ-XRD) and μ-X-ray fluorescence (μ-XRF) with μm-resolution in a laser-heated diamond anvil cell. X-ray diffraction is used to derive the structural changes of the phase reactions whereas X-ray fluorescence gives information on the chemical changes in the sample. In-situ experiments at high pressure and high temperature were performed at beamline P02.2 at PETRA III (Hamburg, Germany) and at beamline ID27 at ESRF (Grenoble, France). In addition to μ-XRD and μ-XRF, ex-situ measurements were made on the recovered sample material using transmission electron microscopy (TEM) and provided further insights into the reaction kinetics of carbonate-silicate reactions. Our investigations show that CaCO3 is unstable in presence of mantle silicates above 1700 K and a reaction takes place in which magnesite plus CaSiO3-perovskite are formed. In addition, we observed that a high content of iron in the carbonate-silicate system favours dolomite formation during the reaction. The subduction of natural carbonates with significant amounts of Sr leads to a comprehensive investigation of the stability not only of CaCO3 phases in contact with mantle silicates but also of SrCO3 (and of Sr-bearing CaCO3). We found that SrCO3 reacts with (Mg,Fe)SiO3-perovskite to form magnesite and gained evidence for the formation of SrSiO3-perovskite. To complement our study on the stability of SrCO3 at conditions of the Earth's lower mantle, we performed powder X-ray diffraction and single crystal X-ray diffraction experiments at ambient temperature and up to 49 GPa. We observed a transformation from SrCO3-I into a new high-pressure phase SrCO3-II at around 26 GPa with Pmmn crystal structure and a bulk modulus of 103(10) GPa. This information is essential to fully understand the phase behaviour and stability of carbonates in the Earth's lower mantle and to elucidate the possibility of introducing Sr into mantle silicates by carbonate-silicate reactions. Simultaneous recording of μ-XRD and μ-XRF in the μm-range over the heated areas provides spatial information not only about phase reactions but also on the elemental redistribution during the reactions. A comparison of the spatial intensity distribution of the XRF signal before and after heating indicates a change in the elemental distribution of Sr and an increase in Sr-concentration was found around the newly formed SrSiO3-perovskite. With the help of additional TEM analyses on the quenched sample material the elemental redistribution was studied at a sub-micrometer scale. Contrary to expectations from combined μ-XRD and μ-XRF measurements, we found that La and Eu were not incorporated into the silicate phases, instead they tend to form either isolated oxide phases (e.g. Eu2O3, La2O3) or hydroxyl-bastn{\"a}site (La(CO3)(OH)). In addition, we observed the transformation from (Mg,Fe)SiO3-perovskite to low-pressure clinoenstatite during pressure release. The monoclinic structure (P21/c) of this phase allows the incorporation of Ca as shown by additional EDX analyses and, to a minor extent, Sr too. Based on our experiments, we can conclude that a detection of the trace elements in-situ at high pressure and high temperature remains challenging. However, our first findings imply that silicates may incorporate the trace elements provided by the carbonates and indicate that carbonates may have a major effect on the trace element contents of mantle phases.},
  language  = {en}
}
@phdthesis{Menges2020,
  author    = {Menges, Johanna},
  title     = {Organic Carbon Storage, Transfer and Transformation in the Himalaya},
  school      = {Universit{\"a}t Potsdam},
  pages     = {179},
  year      = {2020},
  abstract  = {The transfer of particulate organic carbon from continents to the ocean is an important component of the global carbon cycle. Transfer to and burial of photosynthetically fixed biospheric organic carbon in marine sediments can effectively sequester atmospheric carbon dioxide over geological timescales. The exhumation and erosion of fossil organic carbon contained in sedimentary rocks, i.e. petrogenic carbon, can result in remineralization, releasing carbon to the atmosphere. In contrast, eroded petrogenic organic carbon that gets transferred back to the ocean and reburied does not affect atmospheric carbon content. Mountain ranges play a key role in this transfer since they can source vast amounts of sediment including particulate organic carbon. Globally, the export of both, biospheric and petrogenic organic carbon has been linked to sediment export. Additionally, short transfer times from mountains to the ocean and high sediment concentrations have been shown to increase the likelihood of organic carbon burial. While the importance of mountain ranges in the organic carbon cycle is now widely recognized, the processes acting within mountain ranges to influence the storage, cycling and mobilization of organic carbon, as well as carbon fluxes from mountain ranges remain poorly constrained. In this thesis, I employ different methods to assess the nature and fate of particulate organic carbon in mountain belts, ranging from the molecular to regional landscape scale. These studies are located along the Trans-Himalayan Kali Gandaki River in Central Nepal. This river traverses all major geological and climatic zones of the Himalaya, from the dry northern Tibetan plateau to the high-relief, monsoon dominated steep High Himalaya and the lower relief and abundant vegetation of the Lesser Himalayan region. First, I document how biospheric organic matter has accumulated during the Holocene in the headwaters of the Kali Gandaki River valley, by combining compound specific isotope measurements with different dating methods and grain size data, and investigate the stability of this organic carbon reservoir on millennial timescales. I show, that around 1.6 ka an eco-geomorphic tipping point occurred leading to a destabilization of the landscape resulting in today's high erosion rates and the excavation of the aged organic carbon reservoir. This study highlights the climatic and geomorphic controls on biospheric organic carbon storage and release from mountain ranges. Second, I systematically investigate the spatial variation of particulate organic carbon fluxes across the Himalaya along the Kali Gandaki River, using bulk stable and radioactive isotopes combined with a new Bayesian modeling approach. The detailed dataset allows the distinction of aged and modern biospheric organic carbon as well as petrogenic organic carbon across the Himalayan mountain range and the investigation of the role of climatic and geomorphic factors in their riverine export. The data suggest a decoupling of the particulate organic carbon from the sediment yield along the Kali Gandaki River, partially driven by climatic and geomorphic processes. In contrast to the suspended sediment, a large part of the particulate organic carbon exported by the river originates from the Tibetan part of the catchment and is dominated by petrogenic organic carbon derived from Jurassic shales with only minor contributions of modern and aged biospheric organic carbon. These findings emphasize the importance of organic carbon source distribution and erosion mechanisms in determining the organic carbon export from mountain ranges. In a third step, I explore the potential of ultra-high resolution mass spectrometry for particulate organic carbon transport studies. I have generated a novel and unprecedented high-resolution molecular dataset, which contains up to 103 molecular formulas of the lipid fraction of particulate organic matter for modern and aged biospheric carbon, petrogenic organic carbon and river sediments. First, I test if this dataset can be used to better resolve different organic carbon sources and to identify new geochemical tracers. Using multivariate statistics, I identify up to 10² characteristic molecular formulas for the major organic carbon sources in the upper part of the Kali Gandaki catchment, and trace their transfer from the surrounding landscape into the river sediment. Second, I test the potential of the molecular dataset to trace molecular transformations along source-to-sink pathways. I identify changes in molecular metrics derived from the dataset, which are characteristic of transformation processes during incorporation of litter into soil, the aging of soil material, and the mobilization of the organic carbon into the river. These two studies demonstrate that high-resolution molecular datasets open a promising analytical window on particulate organic carbon and can provide novel insights into the composition, sourcing and transformation of riverine particulate organic carbon. Collectively, these studies advance our understanding of the processes contributing to the storage and mobilization of organic carbon in the Central Himalaya, the mountain belt that dominates global erosional fluxes. They do so by identifying the major sources of particulate organic carbon to the Trans-Himalayan Kali Gandaki River, by elucidating their sensitivity to climate and geomorphic processes, and by identifying some of the transformations of this material on the molecular scale. As a result, the thesis demonstrates that the amount and composition of organic carbon routed from mountain belts is a function of the dynamic interactions of geologic, biologic, geomorphic and climatic processes within the mountain belt. This understanding will ultimately help in answering whether the build-up and erosion of mountain ranges over geological time represents a net carbon source or sink to the atmosphere. Beyond this, the thesis contributes to our technical ability to characterize organic matter and attribute it to sources by scoping the potential of high-end molecular analysis.},
  language  = {en}
}
@phdthesis{Friese2020,
  author    = {Friese, Andr{\´e}},
  title     = {Biogeochemistry of ferruginous sediments of Lake Towuti, Sulawesi, Indonesia},
  doi       = {10.25932/publishup-47535},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475355},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxiv, 233},
  year      = {2020},
  abstract  = {Ferruginous conditions were a prominent feature of the oceans throughout the Precambrian Eons and thus throughout much of Earth's history. Organic matter mineralization and diagenesis within the ferruginous sediments that deposited from Earth's early oceans likely played a key role in global biogeochemical cycling. Knowledge of organic matter mineralization in ferruginous sediments, however, remains almost entirely conceptual, as modern analogue environments are extremely rare and largely unstudied, to date. Lake Towuti on the island of Sulawesi, Indonesia is such an analogue environment and the purpose of this PhD project was to investigate the rates and pathways of organic matter mineralization in its ferruginous sediments. Lake Towuti is the largest tectonic lake in Southeast Asia and is hosted in the mafic and ultramafic rocks of the East Sulawesi Ophiolite. It has a maximum water depth of 203 m and is weakly thermally stratified. A well-oygenated surface layer extends to 70 m depth, while waters below 130 m are persistently anoxic. Intensive weathering of the ultramafic catchment feeds the lake with large amounts of iron(oxy)hydroxides while the runoff contains only little sulfate, leading to sulfate-poor (< 20 µM) lake water and anoxic ferruginous conditions below 130 m. Such conditions are analogous to the ferruginous water columns that persisted throughout much of the Archean and Proterozoic eons. Short (< 35 cm) sediment cores were collected from different water depths corresponding to different bottom water redox conditions. Also, a drilling campaign of the International Continental Scientific Drilling Program (ICDP) retrieved a 114 m long sediment core dedicated for geomicrobiological investigations from a water depth of 153 m, well below the depth of oxygen penetration at the time of sampling. Samples collected from these sediment cores form the fundament of this thesis and were used to perform a suite of biogeochemical and microbiological analyses. Geomirobiological investigations depend on uncontaminated samples. However, exploration of subsurface environments relies on drilling, which requires the use of a drilling fluid. Drilling fluid infiltration during drilling can not be avoided. Thus, in order to trace contamination of the sediment core and to identify uncontaminated samples for further analyses a simple and inexpensive technique for assessing contamination during drilling operations was developed and applied during the ICDP drilling campaign. This approach uses an aqeous fluorescent pigment dispersion commonly used in the paint industry as a particulate tracer. It has the same physical properties as conventionally used particulate tracers. However, the price is nearly four orders of magnitude lower solving the main problem of particulate tracer approaches. The approach requires only a minimum of equipment and allows for a rapid contamination assessment potentially even directly on site, while the senstitivity is in the range of already established approaches. Contaminated samples in the drill core were identified and not included for further geomicrobiological investigations. Biogeochemical analyses of short sediment cores showed that Lake Towutis sediments are strongly depleted in electron acceptors commonly used in microbial organic matter mineralization (i.e. oxygen, nitrate, sulfate). Still, the sediments harbor high microbial cell densities, which are a function of redox conditions of Lake Towuti's bottom water. In shallow water depths bottom water oxygenation leads to a higher input of labile organic matter and electron acceptors like sulfate and iron, which promotes a higher microbial abundance. Microbial analyses showed that a versatile microbial community with a potential to perform metabolisms related to iron and sulfate reduction, fermentation as well as methanogenesis inhabits Lake Towuti's surface sediments. Biogeochemical investigations of the upper 12 m of the 114 m sediment core showed that Lake Towuti's sediment is extremely rich in iron with total concentrations up to 2500 µmol cm-3 (20 wt. \%), which makes it the natural sedimentary environment with the highest total iron concentrations studied to date. In the complete or near absence of oxygen, nitrate and sulfate, organic matter mineralization in ferruginous sediments would be expected to proceed anaerobically via the energetically most favorable terminal electron acceptors available - in this case ferric iron. Astonishingly, however, methanogenesis is the dominant (>85 \%) organic matter mineralization process in Lake Towuti's sediment. Reactive ferric iron known to be available for microbial iron reduction is highly abundant throughout the upper 12 m and thus remained stable for at least 60.000 years. The produced methane is not oxidized anaerobically and diffuses out of the sediment into the water column. The proclivity towards methanogenesis, in these very iron-rich modern sediments, implies that methanogenesis may have played a more important role in organic matter mineralization thoughout the Precambrian than previously thought and thus could have been a key contributor to Earth's early climate dynamics. Over the whole sequence of the 114 m long sediment core siderites were identified and characterized using high-resolution microscopic and spectroscopic imaging together with microchemical and geochemical analyses. The data show early diagenetic growth of siderite crystals as a response to sedimentary organic matter mineralization. Microchemical zoning was identified in all siderite crystals. Siderite thus likely forms during diagenesis through growth on primary existing phases and the mineralogical and chemical features of these siderites are a function of changes in redox conditions of the pore water and sediment over time. Identification of microchemical zoning in ancient siderites deposited in the Precambrian may thus also be used to infer siderite growth histories in ancient sedimentary rocks including sedimentary iron formations.},
  language  = {en}
}
@phdthesis{Milewski2020,
  author    = {Milewski, Robert},
  title     = {Potential of optical remote sensing for the analysis of salt pan environments},
  doi       = {10.25932/publishup-47373},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473732},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 145},
  year      = {2020},
  abstract  = {Salt pans also termed playas are common landscape features of hydrologically closed basins in arid and semiarid zones, where evaporation significantly exceeds the local precipitation. The analysis and monitoring of salt pan environments is important for the evaluation of current and future impact of these landscape features. Locally, salt pans have importance for the ecosystem, wildlife and human health, and through dust emissions they influence the climate on regional and global scales. Increasing economic exploitation of these environments in the last years, e.g. by brine extraction for raw materials, as well as climate change severely affect the water, material and energy balance of these systems. Optical remote sensing has the potential to characterise salt pan environments and to increase the understanding of processes in playa basins, as well as to assess wider impacts and feedbacks that exist between climate forcing and human intervention in their regions. Remote sensing techniques can provide information for extensive regions on a high temporal basis compared to traditional field samples and ground observations. Specifically, for salt pans that are often challenging to study because of their large size, remote location, and limited accessibility due to missing infrastructure and ephemeral flooding. Furthermore, the availability of current and upcoming hyperspectral remote sensing data opened the opportunity for the analyses of the complex reflectance signatures that relate to the mineralogical mixtures found in the salt pan sediments. However, these new advances in sensor technology, as well as increased data availability currently have not been fully explored for the study of salt pan environments. The potential of new sensors needs to be assessed and state of the art methods need to be adapted and improved to provide reliable information for in depth analysis of processes and characterisation of the recent condition, as well as to support long-term monitoring and to evaluate environmental impacts of changing climate and anthropogenic activity. This thesis provides an assessment of the capabilities of optical remote sensing for the study of salt pan environments that combines the information of hyperspectral data with the increased temporal coverage of multispectral observations for a more complete understanding of spatial and temporal complexity of salt pan environments using the Omongwa salt pan located in the south-west Kalahari as a test site. In particular, hyperspectral data are used for unmixing of the mineralogical surface composition, spectral feature-based modelling for quantification of main crust components, as well as time-series based classification of multispectral data for the assessment of the long-term dynamic and the analysis of the seasonal process regime. The results show that the surface of the Omongwa pan can be categorized into three major crust types based on diagnostic absorption features and mineralogical ground truth data. The mineralogical crust types can be related to different zones of surface dynamic as well as pan morphology that influences brine flow during the pan inundation and desiccation cycles. Using current hyperspectral imagery, as well as simulated data of upcoming sensors, robust quantification of the gypsum component could be derived. For the test site the results further indicate that the crust dynamic is mainly driven by flooding events in the wet season, but it is also influenced by temperature and aeolian activity in the dry season. Overall, the scientific outcomes show that optical remote sensing can provide a wide range of information helpful for the study of salt pan environments. The thesis also highlights that remote sensing approaches are most relevant, when they are adapted to the specific site conditions and research scenario and that upcoming sensors will increase the potential for mineralogical, sedimentological and geomorphological analysis, and will improve the monitoring capabilities with increased data availability.},
  language  = {en}
}
@phdthesis{Senftleben2020,
  author    = {Senftleben, Robin},
  title     = {Earth's magnetic field over the last 1000 years},
  doi       = {10.25932/publishup-47315},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473150},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 104},
  year      = {2020},
  abstract  = {To investigate the reliability and stability of spherical harmonic models based on archeo/-paleomagnetic data, 2000 Geomagnetic models were calculated. All models are based on the same data set but with randomized uncertainties. Comparison of these models to the geomagnetic field model gufm1 showed that large scale magnetic field structures up to spherical harmonic degree 4 are stable throughout all models. Through a ranking of all models by comparing the dipole coefficients to gufm1 more realistic uncertainty estimates were derived than the authors of the data provide. The derived uncertainty estimates were used in further modelling, which combines archeo/-paleomagnetic and historical data. The huge difference in data count, accuracy and coverage of these two very different data sources made it necessary to introduce a time dependent spatial damping, which was constructed to constrain the spatial complexity of the model. Finally 501 models were calculated by considering that each data point is a Gaussian random variable, whose mean is the original value and whose standard deviation is its uncertainty. The final model arhimag1k is calculated by taking the mean of the 501 sets of Gauss coefficients. arhimag1k fits different dependent and independent data sets well. It shows an early reverse flux patch at the core-mantle boundary between 1000 AD and 1200 AD at the location of the South Atlantic Anomaly today. Another interesting feature is a high latitude flux patch over Greenland between 1200 and 1400 AD. The dipole moment shows a constant behaviour between 1600 and 1840 AD. In the second part of the thesis 4 new paleointensities from 4 different flows of the island Fogo, which is part of Cape Verde, are presented. The data is fitted well by arhimag1k with the exception of the value at 1663 of 28.3 microtesla, which is approximately 10 microtesla lower than the model suggest.},
  language  = {en}
}
@phdthesis{Borghini2020,
  author    = {Borghini, Alessia},
  title     = {Melt inclusions in mafic rocks as witnesses of metasomatism in the Bohemian Massif},
  doi       = {10.25932/publishup-47363},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473639},
  school      = {Universit{\"a}t Potsdam},
  pages     = {205},
  year      = {2020},
  abstract  = {Orogenic peridotites represent portions of upper subcontinental mantle now incorporated in mountain belts. They often contain layers, lenses and irregular bodies of pyroxenite and eclogite. The origin of this heterogeneity and the nature of these layers is still debated but it is likely to involve processes such as transient melts coming from the crust or the mantle and segregating in magma conduits, crust-mantle interaction, upwelling of the asthenosphere and metasomatism. All these processes occur in the lithospheric mantle and are often related with the subduction of crustal rocks to mantle depths. In fact, during subduction, fluids and melts are released from the slab and can interact with the overlying mantle, making the study of deep melts in this environment crucial to understand mantle heterogeneity and crust-mantle interaction. The aim of this thesis is precisely to better constrain how such processes take place studying directly the melt trapped as primary inclusions in pyroxenites and eclogites. The Bohemian Massif, crystalline core of the Variscan belt, is targeted for these purposes because it contains orogenic peridotites with layers of pyroxenite and eclogite and other mafic rocks enclosed in felsic high pressure and ultra-high pressure crustal rocks. Within this Massif mafic rocks from two areas have been selected: the garnet clinopyroxenite in orogenic peridotite of the Granulitgebirge and the ultra-high pressure eclogite in the diamond-bearing gneisses of the Erzgebirge. In both areas primary melt inclusions were recognized in the garnet, ranging in size between 2-25 µm and with different degrees of crystallization, from glassy to polycrystalline. They have been investigated with Micro Raman spectroscopy and EDS mapping and the mineral assemblage is kumdykolite, phlogopite, quartz, kokchetavite, phase with a main Raman peak at 430 cm-1, phase with a main Raman peak at 412 cm-1, white mica and calcite with some variability in relative abundance depending on the case study. In the Granulitgebirge osumilite and pyroxene are also present, whereas calcite is one of the main phases in the Erzgebirge. The presence of glass and the mineral assemblage in the nanogranitoids suggest that they were former droplets of melt trapped in the garnet while it was growing. Glassy inclusions and re-homogenized nanogranitoids show a silicate melt that is granitic, hydrous, high in alkalis and weakly peraluminous. The melt is also enriched in both case studies in Cs, Pb, Rb, U, Th, Li and B suggesting the involvement of crustal component, i.e. white mica (main carrier of Cs, Pb, Rb, Li and B), and a fluid (Cs, Th and U) in the melt producing reaction. The whole rock in both cases mainly consists of garnet and clinopyroxene with, in Erzgebirge samples, the additional presence of quartz both in the matrix and as a polycrystalline inclusion in the garnet. The latter is interpreted as a quartz pseudomorph after coesite and occurs in the same microstructural position as the melt inclusions. Both rock types show a crustal and subduction zone signature with garnet and clinopyroxene in equilibrium. Melt was likely present during the metamorphic peak of the rock, as it occurs in garnet. Our data suggest that the processes most likely responsible for the formation of the investigated rocks in both areas is a metasomatic reaction between a melt produced in the crust and mafic layers formerly located in the mantle wedge for the Granulitgebirge and in the subducted continental crust itself in the Erzgebirge. Thus metasomatism in the first case took place in the mantle overlying the slab, whereas in the second case metasomatism took place in the continental crust that already contained, before subduction, mafic layers. Moreover, the presence of former coesite in the same microstructural position of the melt inclusions in the Erzgebirge garnets suggest that metasomatism took place at ultra-high pressure conditions. Summarizing, in this thesis we provide new insights into the geodynamic evolution of the Bohemian Massif based on the study of melt inclusions in garnet in two different mafic rock types, combining the direct microstructural and geochemical investigation of the inclusions with the whole-rock and mineral geochemistry. We report for the first time data, directly extracted from natural rocks, on the metasomatic melt responsible for the metasomatism of several areas of the Bohemian Massif. Besides the two locations here investigated, belonging to the Saxothuringian Zone, a signature similar to the investigated melt is clearly visible in pyroxenite and peridotite of the T-7 borehole (again Saxothuringian Zone) and the durbachite suite located in the Moldanubian Zone.},
  language  = {en}
}
@phdthesis{Zeckra2020,
  author    = {Zeckra, Martin},
  title     = {Seismological and seismotectonic analysis of the northwestern Argentine Central Andean foreland},
  doi       = {10.25932/publishup-47324},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 120},
  year      = {2020},
  abstract  = {After a severe M W 5.7 earthquake on October 17, 2015 in El Galp{\´o}n in the province of Salta NW Argentina, I installed a local seismological network around the estimated epicenter. The network covered an area characterized by inherited Cretaceous normal faults and neotectonic faults with unknown recurrence intervals, some of which may have been reactivated normal faults. The 13 three-component seismic stations recorded data continuously for 15 months. The 2015 earthquake took place in the Santa B{\´a}rbara System of the Andean foreland, at about 17km depth. This region is the easternmost morphostructural region of the central Andes. As a part of the broken foreland, it is bounded to the north by the Subandes fold-and-thrust belt and the Sierras Pampeanas to the south; to the east lies the Chaco-Paran{\´a} basin. A multi-stage morphotectonic evolution with thick-skinned basement uplift and coeval thin-skinned deformation in the intermontane basins is suggested for the study area. The release of stresses associated with the foreland deformation can result in strong earthquakes, as the study area is known for recurrent and historical, destructive earthquakes. The available continuous record reaches back in time, when the strongest event in 1692 (magnitude 7 or intensity IX) destroyed the city of Esteco. Destructive earthquakes and surface deformation are thus a hallmark of this part of the Andean foreland. With state-of-the-art Python packages (e.g. pyrocko, ObsPy), a semi-automatic approach is followed to analyze the collected continuous data of the seismological network. The resulting 1435 hypocenter locations consist of three different groups: 1.) local crustal earthquakes (nearly half of the events belong to this group), 2.) interplate activity, of regional distance in the slab of the Nazca-plate, and 3.) very deep earthquakes at about 600km depth. My major interest focused on the first event class. Those crustal events are partly aftershock events of the El Galp{\´o}n earthquake and a second earthquake, in the south of the same fault. Further events can be considered as background seismicity of other faults within the study area. Strikingly, the seismogenic zone encompass the whole crust and propagates brittle deformation down, close to the Moho. From the collected seismological data, a local seismic velocity model is estimated, using VELEST. After the execution of various stability tests, the robust minimum 1D-velocity model implies guiding values for the composition of the local, subsurface structure of the crust. Afterwards, performing a hypocenter relocation enables the assignment of individual earthquakes to aftershock clusters or extended seismotectonic structures. This allows the mapping of previously unknown seismogenic faults. Finally, focal mechanisms are modeled for events with acurately located hypocenters, using the newly derived local velocity model. A compressive regime is attested by the majority of focal mechanisms, while the strike direction of the individual seismogenic structures is in agreement with the overall north - south orientation of the Central Andes, its mountain front, and individual mountain ranges in the southern Santa-B{\´a}rbara-System.},
  language  = {en}
}
@phdthesis{Nardini2020,
  author    = {Nardini, Livia},
  title     = {Influence of heterogeneities on the initiation of shear zones in the ductile regime},
  doi       = {10.25932/publishup-44616},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-446165},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIX, 121},
  year      = {2020},
  abstract  = {The current thesis contains the results from two experimental and one modelling study focused on the topic of ductile strain localization in the presence of material heterogeneities. Localization of strain in the high temperature regime is a well known feature of rock deformation occurring in nature at different scales and in a variety of lithologies. Large scale shear zones at the roots of major crustal fault zones are considered responsible for the activity of plate tectonics on our planet. A large number of mechanisms are suggested to be associated with strain softening and nucleation of localization. Among these, the presence of material heterogeneities within homogeneous host rocks is frequently observed in field examples to trigger shear zone development. Despite a number of studies conducted on the topic, the mechanisms controlling initiation and evolution of localization are not fully understood yet. We investigated, experimentally and by means of numerical modelling, phenomenological and microphysical aspects of high temperature strain localization in a homogeneous body containing single and paired inclusions of weaker material. A monomineralic carbonate system composed of Carrara marble (homogeneous, strong matrix) and Solnhofen limestone (weak planar inclusions) is selected for our studies based on its versatility as an experimental material and on the frequent occurrence of carbonate rocks at the core of natural shear zones. To explore the influence of different loading conditions on heterogeneity-induced high temperature shear zones we conducted torsion experiments under constant twist (deformation) rate and constant torque (stress) conditions in a Paterson-type deformation apparatus on hollow cylinders of marble containing single planar inclusions of limestone. At the imposed experimental conditions (900 ◦C temperature and 400 MPa confining pressure) both materials deform plastically and the marble is ≈ 9 times stronger than the limestone. The viscosity contrast between the two materials induces a perturbation of the stress field within the marble matrix at the tip of the planar inclusion. Early on along the deformation path (at bulk shear strains ≈ 0.3), heterogeneous distribution of strain can be observed under both loading conditions and a small area of incipient strain localization is formed at the tip of the weak limestone inclusion. Strongly deformed grains, incipient dynamic recrystallization and a weak crystallographic preferred orientation characterize the marble within an area a few mm in front of the inclusion. As the bulk strain is increased (up to γ ≈ 1), the area of microstructural modification is expanded along the inclusion plane, the texture strengthens and grain size refinement by dynamic recrystallization becomes pervasive. Locally, evidences for coexisting brittle deformation are also observed regardless of the imposed loading conditions. A shear zone is effectively formed within the deforming Carrara marble, its geometry controlled by the plane containing the thin plate of limestone. Thorough microstructural and textural analysis, however, do not reveal substantial differences in the mechanisms or magnitude of strain localization at the different loading conditions. We conclude that, in the presence of material heterogeneities capable of inducing strain softening, the imposed loading conditions do not affect ductile localization in its nucleating and transient stages. As the ultimate goal of experimental rock deformation is the extrapolation of results to geologically relevant time and space scales, we developed 2D numerical models reproducing (and benchmarked to) our experimental results. Our cm-scaled models have been implemented with a first-order strain-dependent softening law to reproduce the effect of rheological weakening in the deforming material. We successfully reproduced the local stress concentration at the inclusion tips and the strain localization initiated in the marble matrix. The heterogeneous distribution of strain and its evolution with imposed bulk deformation (i.e. the shape and extent of the nucleating shear zone) are observed to depend on the degree of softening imposed to the deforming matrix. When a second (artificial) softening step is introduced at elevated bulk strains in the model, the formation of a secondary high strain layer is observed at the core of the initial shear zone, analogous to the development of ultramylonite bands in high strain natural shear zones. Our results do not only reproduce the nucleation and transient evolution of a heterogeneity-induced high temperature shear zone with high accuracy, but also confirm the importance of introducing reliable softening laws capable of mimicking strain weakening to numerical models of crustal scale ductile processes. Material heterogeneities inducing strain localization in the field are often consisting of brittle precursors (joints and fractures). More generally, the interaction of brittle and ductile deformation mechanisms and its effect on the localization of strain have been a key topic in the structural geology community for a long time. The positive feedback between (micro)fracturing and ductile strain localization is a well recognized effect in a number of field examples. We experimentally investigated the influence of brittle deformation on the initiation and evolution of high temperature shear zones in a strong matrix containing pairs of weak material heterogeneities. Our Carrara marble-Solnhofen limestone inclusions system was tested in triaxial compression under constant strain rate and high temperature (900 ◦C) conditions in a Paterson deformation apparatus. The inclusion pairs were arranged in non-overlapping step-over geometries of either compressional or extensional nature. Experimental runs were conducted at different confining pressures (30, 50, 100 and 300 MPa) to induce various amounts of brittle deformation within the marble matrix. At low confinement (30 and 50 MPa) abundant brittle deformation is observed in all configurations, but the spatial distribution of cracks is dependent on the kinematics of the step-over region: concentrated along the shearing plane between the inclusions in the extensional samples, or broadly distributed around the inclusions but outside the step-over region in the compressional configuration. Accordingly, brittle-assisted ductile processes tend to localize deformation along the inclusions plane in the extensional geometry or to distribute widely across large areas of the matrix in the compressional step-over. At pressures of 100 and 300 MPa fracturing is mostly suppressed in both configurations and strain is accommodated almost entirely by viscous creep. In extensional samples this leads to progressive de-localization with increasing confinement. Our results show that, while ductile localization of strain is indeed more efficient where assisted by brittle processes, these latter are only effective if themselves heterogeneously distributed, ultimately a function of the local stress perturbations.},
  language  = {en}
}
@phdthesis{RamezaniZiarani2020,
  author    = {Ramezani Ziarani, Maryam},
  title     = {Characterization of atmospheric processes related to hydro-meteorological extreme events over the south-central Andes},
  doi       = {10.25932/publishup-47175},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-471755},
  school      = {Universit{\"a}t Potsdam},
  pages     = {i, 88},
  year      = {2020},
  abstract  = {The significant environmental and socioeconomic consequences of hydrometeorological extreme events, such as extreme rainfall, are constituted as a most important motivation for analyzing these events in the south-central Andes of NW Argentina. The steep topographic and climatic gradients and their interactions frequently lead to the formation of deep convective storms and consequently trigger extreme rainfall generation. In this dissertation, I focus on identifying the dominant climatic variables and atmospheric conditions and their spatiotemporal variability leading to deep convection and extreme rainfall in the south-central Andes. This dissertation first examines the significant contribution of temperature on atmospheric humidity (dew-point temperature, Td) and on convection (convective available potential energy, CAPE) for deep convective storms and hence, extreme rainfall along the topographic and climatic gradients. It was found that both climatic variables play an important role in extreme rainfall generation. However, their contributions differ depending on topographic and climatic sub-regions, as well as rainfall percentiles. Second, this dissertation explores if (near real-time) the measurements conducted by the Global Navigation Satellite System (GNSS) on integrated water vapor (IWV) provide reliable data for explaining atmospheric humidity. I argue that GNSS-IWV, in conjunction with other atmospheric stability parameters such as CAPE, is able to decipher the extreme rainfall in the eastern central Andes. In my work, I rely on a multivariable regression analysis described by a theoretical relationship and fitting function analysis. Third, this dissertation identifies the local impact of convection on extreme rainfall in the eastern Andes. Relying on a Principal Component Analysis (PCA) it was found that during the existence of moist and warm air, extreme rainfall is observed more often during local night hours. The analysis includes the mechanisms for this observation. Exploring the atmospheric conditions and climatic variables leading to extreme rainfall is one of the main findings of this dissertation. The conditions and variables are a prerequisite for understanding the dynamics of extreme rainfall and predicting these events in the eastern Andes.},
  language  = {en}
}
@phdthesis{Pick2020,
  author    = {Pick, Leonie Johanna Lisa},
  title     = {The centennial evolution of geomagnetic activity and its driving mechanisms},
  doi       = {10.25932/publishup-47275},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472754},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 135},
  year      = {2020},
  abstract  = {This cumulative thesis is concerned with the evolution of geomagnetic activity since the beginning of the 20th century, that is, the time-dependent response of the geomagnetic field to solar forcing. The focus lies on the description of the magnetospheric response field at ground level, which is particularly sensitive to the ring current system, and an interpretation of its variability in terms of the solar wind driving. Thereby, this work contributes to a comprehensive understanding of long-term solar-terrestrial interactions. The common basis of the presented publications is formed by a reanalysis of vector magnetic field measurements from geomagnetic observatories located at low and middle geomagnetic latitudes. In the first two studies, new ring current targeting geomagnetic activity indices are derived, the Annual and Hourly Magnetospheric Currents indices (A/HMC). Compared to existing indices (e.g., the Dst index), they do not only extend the covered period by at least three solar cycles but also constitute a qualitative improvement concerning the absolute index level and the ~11-year solar cycle variability. The analysis of A/HMC shows that (a) the annual geomagnetic activity experiences an interval-dependent trend with an overall linear decline during 1900-2010 of ~5 \% (b) the average trend-free activity level amounts to ~28 nT (c) the solar cycle related variability shows amplitudes of ~15-45 nT (d) the activity level for geomagnetically quiet conditions (Kp<2) lies slightly below 20 nT. The plausibility of the last three points is ensured by comparison to independent estimations either based on magnetic field measurements from LEO satellite missions (since the 1990s) or the modeling of geomagnetic activity from solar wind input (since the 1960s). An independent validation of the longterm trend is problematic mainly because the sensitivity of the locally measured geomagnetic activity depends on geomagnetic latitude. Consequently, A/HMC is neither directly comparable to global geomagnetic activity indices (e.g., the aa index) nor to the partly reconstructed open solar magnetic flux, which requires a homogeneous response of the ground-based measurements to the interplanetary magnetic field and the solar wind speed. The last study combines a consistent, HMC-based identification of geomagnetic storms from 1930-2015 with an analysis of the corresponding spatial (magnetic local time-dependent) disturbance patterns. Amongst others, the disturbances at dawn and dusk, particularly their evolution during the storm recovery phases, are shown to be indicative of the solar wind driving structure (Interplanetary Coronal Mass Ejections vs. Stream or Co-rotating Interaction Regions), which enables a backward-prediction of the storm driver classes. The results indicate that ICME-driven geomagnetic storms have decreased since 1930 which is consistent with the concurrent decrease of HMC. Out of the collection of compiled follow-up studies the inclusion of measurements from high-latitude geomagnetic observatories into the third study's framework seems most promising at this point.},
  language  = {en}
}
@phdthesis{RodriguezZuluaga2020,
  author    = {Rodriguez Zuluaga, Juan},
  title     = {Electric and magnetic characteristics of equatorial plasma depletions},
  doi       = {10.25932/publishup-44587},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445873},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 87},
  year      = {2020},
  abstract  = {Near-Earth space represents a significant scientific and technological challenge. Particularly at magnetic low-latitudes, the horizontal magnetic field geometry at the dip equator and its closed field-lines support the existence of a distinct electric current system, abrupt electric field variations and the development of plasma irregularities. Of particular interest are small-scale irregularities associated with equatorial plasma depletions (EPDs). They are responsible for the disruption of trans-ionospheric radio waves used for navigation, communication, and Earth observation. The fast increase of satellite missions makes it imperative to study the near-Earth space, especially the phenomena known to harm space technology or disrupt their signals. EPDs correspond to the large-scale structure (i.e., tens to hundreds of kilometers) of topside F region irregularities commonly known as Spread F. They are observed as depleted-plasma density channels aligned with the ambient magnetic field in the post-sunset low-latitude ionosphere. Although the climatological variability of their occurrence in terms of season, longitude, local time and solar flux is well-known, their day to day variability is not. The sparse observations from ground-based instruments like radars and the few simultaneous measurements of ionospheric parameters by space-based instruments have left gaps in the knowledge of EPDs essential to comprehend their variability. In this dissertation, I profited from the unique observations of the ESA's Swarm constellation mission launched in November 2013 to tackle three issues that revealed novel and significant results on the current knowledge of EPDs. I used Swarm's measurements of the electron density, magnetic, and electric fields to answer, (1.) what is the direction of propagation of the electromagnetic energy associated with EPDs?, (2.) what are the spatial and temporal characteristics of the electric currents (field-aligned and diamagnetic currents) related to EPDs, i.e., seasonal/geographical, and local time dependencies?, and (3.) under what conditions does the balance between magnetic and plasma pressure across EPDs occur? The results indicate that: (1.) The electromagnetic energy associated with EPDs presents a preference for interhemispheric flows; that is, the related Poynting flux directs from one magnetic hemisphere to the other and varies with longitude and season. (2.) The field-aligned currents at the edges of EPDs are interhemispheric. They generally close in the hemisphere with the highest Pedersen conductance. Such hemispherical preference presents a seasonal/longitudinal dependence. The diamagnetic currents increase or decrease the magnetic pressure inside EPDs. These two effects rely on variations of the plasma temperature inside the EPDs that depend on longitude and local time. (3.) EPDs present lower or higher plasma pressure than the ambient. For low-pressure EPDs the plasma pressure gradients are mostly dominated by variations of the plasma density so that variations of the temperature are negligible. High-pressure EPDs suggest significant temperature variations with magnitudes of approximately twice the ambient. Since their occurrence is more frequent in the vicinity of the South Atlantic magnetic anomaly, such high temperatures are suggested to be due to particle precipitation. In a broader context, this dissertation shows how dedicated satellite missions with high-resolution capabilities improve the specification of the low-latitude ionospheric electrodynamics and expand knowledge on EPDs which is valuable for current and future communication, navigation, and Earth-observing missions. The contributions of this investigation represent several 'firsts' in the study of EPDs: (1.) The first observational evidence of interhemispheric electromagnetic energy flux and field-aligned currents. (2.) The first spatial and temporal characterization of EPDs based on their associated field-aligned and diamagnetic currents. (3.) The first evidence of high plasma pressure in regions of depleted plasma density in the ionosphere. These findings provide new insights that promise to advance our current knowledge of not only EPDs but the low-latitude post-sunset ionosphere environment.},
  language  = {en}
}
@phdthesis{Schimpf2020,
  author    = {Schimpf, Stefan},
  title     = {Herkunft und Ablagerungsmilieu quart{\"a}rer Sedimente im Einzugsgebiet des Heihe, NW China},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 186},
  year      = {2020},
  abstract  = {Der zentralasiatische Naturraum, wie er sich uns heute pr{\"a}sentiert, ist das Ergebnis eines Zusammenwirkens vieler verschiedener Faktoren {\"u}ber Jahrmillionen hinweg. Im aktuellen Kontext des Klimawandels zeigt sich jedoch, wie stark sich Stofffl{\"u}sse auch kurzfristig {\"a}ndern und dabei das Gesicht der Landschaft verwandeln k{\"o}nnen. Die Gobi-W{\"u}ste in der Inneren Mongolei (China), als Teil der gleichnamigen Trockenregionen Nordwestchinas, ist aufgrund der Ausgestaltung ihrer landschaftspr{\"a}genden Elemente sowie ihrer Landschaftsdynamik, im Zusammenhang mit der Lage zum Tibet-Plateau, in den Fokus der klimageschichtlichen Grundlagenforschung ger{\"u}ckt. Als großes Langzeitarchiv unterschiedlichster fluvialer, lakustriner und {\"a}olischer Sedimente stellt sie eine bedeutende Lokalit{\"a}t zur Rekonstruktion von lokalen und regionalen Stofffl{\"u}ssen dar.. Andererseits ist die Gobi-W{\"u}ste zugleich auch eine bedeutende Quelle f{\"u}r den {\"u}berregionalen Staubtransport, da sie aufgrund der klimatischen Bedingungen insbesondere der Erosion durch Ausblasung preisgegeben wird. Vor diesem Hintergrund erfolgten zwischen 2011 und 2014, im Rahmen des BMBF-Verbundprogramms WTZ Zentralasien - Monsundynamik \& Geo{\"o}kosysteme (F{\"o}rderkennzeichen 03G0814), mehrere deutsch-chinesische Expeditionen in das Ejina-Becken (Innere Mongolei) und das Qilian Shan-Vorland. Im Zuge dieser Expeditionen wurden f{\"u}r eine Bestimmung potenzieller Sedimentquellen erstmals zahlreiche Oberfl{\"a}chenproben aus dem gesamten Einzugsgebiet des Heihe (schwarzer Fluss) gesammelt. Zudem wurden mit zwei Bohrungen im inneren des Ejina-Beckens, erg{\"a}nzende Sedimentbohrkerne zum bestehenden Bohrkern D100 (siehe W{\"u}nnemann (2005)) abgeteuft, um weit reichende, erg{\"a}nzende Informationen zur Landschaftsgeschichte und zum {\"u}berregionalen Sedimenttransfer zu erhalten. Gegenstand und Ziel der vorliegenden Doktorarbeit ist die sedimentologisch-mineralogische Charakterisierung des Untersuchungsgebietes in Bezug auf potenzielle Sedimentquellen und Stofffl{\"u}sse des Ejina-Beckens sowie die Rekonstruktion der Ablagerungsgeschichte eines dort erbohrten, 19m langen Sedimentbohrkerns (GN100). Schwerpunkt ist hierbei die Kl{\"a}rung der Sedimentherkunft innerhalb des Bohrkerns sowie die Ausweisung von Herkunftssignalen und m{\"o}glichen Sedimentquellen bzw. Sedimenttransportpfaden. Die methodische Herangehensweise basiert auf einem Multi-Proxy-Ansatz zur Charakterisierung der klastischen Sedimentfazies anhand von Gel{\"a}ndebeobachtungen, lithologisch-granulometrischen und mineralogisch-geochemischen Analysen sowie statistischen Verfahren. F{\"u}r die mineralogischen Untersuchungen der Sedimente wurde eine neue, rasterelektronenmikroskopische Methode zur automatisierten Partikelanalyse genutzt und den traditionellen Methoden gegen{\"u}bergestellt. Die synoptische Betrachtung der granulometrischen, geochemischen und mineralogischen Befunde der Oberfl{\"a}chensedimente ergibt f{\"u}r das Untersuchungsgebiet ein logisches Kaskadenmodell mit immer wiederkehrenden Prozessbereichen und {\"a}hnlichen Prozesssignalen. Die umfangreichen granulometrischen Analysen deuten dabei auf abnehmende Korngr{\"o}ßen mit zunehmender Entfernung vom Qilian Shan hin und erm{\"o}glichen die Identifizierung von vier texturellen Signalen: den fluvialen Sanden, den D{\"u}nensanden, den Stillwassersedimenten und St{\"a}uben. Diese Ergebnisse k{\"o}nnen als Interpretationsgrundlage f{\"u}r die Korngr{\"o}ßenanalysen des Bohrkerns genutzt werden. Somit ist es m{\"o}glich, die Ablagerungsgeschichte der Bohrkernsedimente zu rekonstruieren und in Verbindung mit eigenen und literaturbasierten Datierungen in einen Gesamtkontext einzuh{\"a}ngen. F{\"u}r das Untersuchungsgebiet werden somit vier Ablagerungsphasen ausgewiesen, die bis in die Zeit des letzten glazialen Maximums (LGM) zur{\"u}ckreichen. W{\"a}hrend dieser Ablagerungsphasen kam es im Zuge unterschiedlicher Aktivit{\"a}ts- und Stabilit{\"a}tsphasen zu einer kontinuierlichen Progradation und {\"U}berpr{\"a}gung des Schwemmf{\"a}chers. Eine besonders aktive Phase kann zwischen 8 ka und 4 ka BP festgestellt werden, w{\"a}hrend der es aufgrund zunehmender fluvialer Aktivit{\"a}ten zu einer deutlich verst{\"a}rkten Schwemmf{\"a}cherdynamik gekommen zu sein scheint. In den Abschnitten davor und danach waren es vor allem {\"a}olische Prozesse, die zu einer {\"U}berpr{\"a}gung des Schwemmf{\"a}chers gef{\"u}hrt haben. Hinsichtlich der mineralogischen Herkunftssignale gibt es eine große Variabilit{\"a}t. Dies spiegelt die enorme Heterogenit{\"a}t der Geologie des Untersuchungsgebietes wider, wodurch die r{\"a}umlichen Signale nicht sehr stark ausgepr{\"a}gt sind. Dennoch, k{\"o}nnen f{\"u}r das Einzugsgebiet drei gr{\"o}ßere Bereiche deklariert werden, die als Herkunftsgebiet in Frage kommen. Das {\"o}stliche Qilian Shan Vorland zeichnet sich dabei durch deutlich h{\"o}here Chloritgehalte als prim{\"a}re Quelle f{\"u}r die Sedimente im Ejina-Becken aus. Sie unterscheiden sich insbesondere durch stark divergierende Chloritgehalte in der Tonmineral- und Gesamtmineralfraktion, was das {\"o}stliche Qilian Shan Vorland als prim{\"a}re Quelle f{\"u}r die Sedimente im Ejina-Becken auszeichnet. Dies steht in Zusammenhang mit den Gr{\"u}nschiefern, Ophioliten und Serpentiniten in diesem Bereich. Geochemisch deutet vor allem das Cr/Rb-Verh{\"a}ltnis eine große Variabilit{\"a}t innerhalb des Einzugsgebietes an. Auch hier ist es das {\"o}stliche Vorland, welches aufgrund seines hohen Anteils an mafischen Gesteinen reich an Chromiten und Spinellen ist und sich somit vom restlichen Untersuchungsgebiet abhebt. Die zeitliche aber auch die generelle Variabilit{\"a}t der Sedimentherkunft l{\"a}sst sich in den Bohrkernsedimenten nicht so deutlich nachzeichnen. Die mineralogisch-sedimentologischen Eigenschaften der erbohrten klastischen Sedimente zeugen zwar von zwischenzeitlichen {\"A}nderungen bei der Sedimentherkunft, diese sind jedoch nicht so deutlich ausgepr{\"a}gt, wie es die Quellsignale in den Oberfl{\"a}chensedimenten vermuten lassen. Ein Grund daf{\"u}r scheint die starke Vermischung unterschiedlichster Sedimente w{\"a}hrend des Transportes zu sein. Die Kombination der Korngr{\"o}ßenergebnisse mit den Befunden der Gesamt- und Schwermineralogie deuten darauf hin, dass es zwischenzeitlich eine Phase mit {\"u}berwiegend {\"a}olischen Prozessen gegeben hat, die mit einem Sedimenteintrag aus dem westlichen Bei Shan in Verbindung stehen. Neben der Zunahme ultrastabiler Schwerminerale wie Zirkon und Granat und der Abnahme opaker Schwerminerale, weisen vor allem die heutigen Verh{\"a}ltnisse darauf hin. Der Vergleich der traditionellen Schwermineralanalyse mit der Computer-Controlled-Scanning-Electron-Microscopy (kurz: CCSEM), die eine automatisierte Partikelauswertung der Proben erm{\"o}glicht, zeigt den deutlichen Vorteil der modernen Analysemethode. Neben einem zeitlichen Vorteil, den man durch die automatisierte Abarbeitung der vorbereiteten Proben erlangen kann, steht vor allem die deutlich gr{\"o}ßere statistische Signifikanz des Ergebnisses im Vordergrund. Zudem k{\"o}nnen mit dieser Methode auch chemische Variet{\"a}ten einiger Schwerminerale bestimmt werden, die eine noch feinere Klassifizierung und sicherere Aussagen zu einer m{\"o}glichen Sedimentherkunft erm{\"o}glichen. Damit ergeben sich außerdem verbesserte Aussagen zu Zusammensetzungen und Entstehungsprozessen der abgelagerten Sedimente. Die Studie verdeutlicht, dass die Sedimentherkunft innerhalb des Untersuchungsgebietes sowie die ablaufenden Prozesse zum Teil stark von lokalen Gegebenheiten abh{\"a}ngen. Die Heterogenit{\"a}t der Geologie und die Gr{\"o}ße des Einzugsgebietes sowie die daraus resultierende Komplexit{\"a}t der Sedimentgenese, machen exakte Zuordnungen zu klar definierten Sedimentquellen sehr schwer. Dennoch zeigen die Ergebnisse, dass die Sedimentzufuhr in das Ejina-Becken in erster Linie durch fluviale klastische Sedimente des Heihe aus dem Qilian Shan erfolgt sein muss. Die Untersuchungsergebnisse zeigen jedoch ebenso die Notwendigkeit einer erg{\"a}nzenden Bearbeitung angrenzender Untersuchungsgebiete, wie beispielsweise den Gobi-Altai im Norden oder den Beishan im Westen, sowie die Verdichtung der Oberfl{\"a}chenbeprobung zur feineren Aufl{\"o}sung von lokalen Sedimentquellen.},
  language  = {de}
}
@phdthesis{Liu2020,
  author    = {Liu, Sibiao},
  title     = {Controls of foreland-deformation patterns in the orogen-foreland shortening system},
  doi       = {10.25932/publishup-44573},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445730},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 150},
  year      = {2020},
  abstract  = {The Andean Plateau (Altiplano-Puna Plateau) of the southern Central Andes is the second-highest orogenic plateau on our planet after Tibet. The Andean Plateau and its foreland exhibit a pronounced segmentation from north to south regarding the style and magnitude of deformation. In the Altiplano (northern segment), more than 300 km of tectonic shortening has been recorded, which started during the Eocene. A well-developed thin-skinned thrust wedge located at the eastern flank of the plateau (Subandes) indicates a simple-shear shortening mode. In contrast, the Puna (southern segment) records approximately half of the shortening of the Altiplano - and the shortening started later. The tectonic style in the Puna foreland switches to a thick-skinned mode, which is related to pure-shear shortening. In this study, carried out in the framework of the StRATEGy project, high-resolution 2D thermomechanical models were developed to systematically investigate controls of deformation patterns in the orogen-foreland pair. The 2D and 3D models were subsequently applied to study the evolution of foreland deformation and surface topography in the Altiplano-Puna Plateau. The models demonstrate that three principal factors control the foreland-deformation patterns: (i) strength differences in the upper lithosphere between the orogen and its foreland, rather than a strength difference in the entire lithosphere; (ii) gravitational potential energy of the orogen (GPE) controlled by crustal and lithospheric thicknesses, and (iii) the strength and thickness of foreland-basin sediments. The high-resolution 2D models are constrained by observations and successfully reproduce deformation structures and surface topography of different segments of the Altiplano-Puna plateau and its foreland. The developed 3D models confirm these results and suggest that a relatively high shortening rate in the Altiplano foreland (Subandean foreland fold-and-thrust belt) is due to simple-shear shortening facilitated by thick and mechanically weak sediments, a process which requires a much lower driving force than the pure-shear shortening deformation mode in the adjacent broken foreland of the Puna, where these thick sedimentary basin fills are absent. Lower shortening rate in the Puna foreland is likely accommodated in the forearc by the slab retreat.},
  language  = {en}
}
@phdthesis{KaramzadehToularoud2020,
  author    = {Karamzadeh Toularoud, Nasim},
  title     = {Earthquake source and receiver array optimal configuration},
  doi       = {10.25932/publishup-45982},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459828},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 94},
  year      = {2020},
  abstract  = {Seismic receiver arrays have variety of applications in seismology, particularly when the signal enhancement is a prerequisite to detect seismic events, and in situations where installing and maintaining sparse networks are impractical. This thesis has mainly focused on the development of a new approach for seismological source and receiver array design.The proposed approach deals with the array design task as an optimization problem. The criteria and prerequisite constraints in array design task are integrated in objective function definition and evaluation of a optimization process. Three cases are covered in this thesis: (1) a 2-D receiver array geometry optimization, (2) a 3-D source array optimization, and (3) an array application to monitor microseismic data, where the effect of different types of noise are evaluated. A flexible receiver array design framework implements a customizable scenario modelling and optimization scheme by making use of synthetic seismograms. Using synthetic seismograms to evaluate array performance makes it possible to consider additional constraints, e.g. land ownership, site-specific noise levels or characteristics of the seismic sources under investigation. The use of synthetic array beamforming as an array design criteria is suggested. The framework is customized by designing a 2-D small scale receiver array to monitor earthquake swarm activity in northwest Bohemia/ Vogtland in central Europe. Two sub-functions are defined to verify the accuracy of horizontal slowness estimation; one to suppress aliasing effects due to possible secondary lobes of synthetic array beamforming calculated in horizontal slowness space, and the other to reduce the event's mislocation caused by miscalculation of the horizontal slowness vector. Subsequently, a weighting technique is applied to combine the sub-functions into one single scalar objective function to use in the optimization process. The idea of optimal array is employed to design a 3-D source array, given a well-located catalog of events. The conditions to make source arrays are formulated in four objective functions and a weighted sum technique is used to combine them in one single scalar function. The criteria are: (1) accurate slowness vector estimation, (2) high waveform coherency, (3) low location error and (4) high energy of coda phases. The method is evaluated by two experiments, (1) a synthetic test using realistic synthetic seismograms, (2) using real seismograms, and for each case optimized SA elements are configured using the data from the Vogtland area. The location of a possible scatterer in the velocity model, that makes the converted/reflected phases, e.g. sp-phases, is retrieved by a grid search method using the optimized SA. The accuracy of the approach and the obtained results demonstrated that the method is applicable to study the crustal structure and the location of crustal scatterers when the strong converted phases are observed in the data and a well-located catalog is available. Small aperture arrays are employed in seismology for a variety of applications, ranging from pure event detection to monitor and study of microcosmic activities. The monitoring of microseismicity during temporary human activities is often difficult, as the signal-to-noise ratio is very low and noise is strongly increased during the operation. The combination of small aperture seismic arrays with shallow borehole sensors offers a solution. We tested this monitoring approach at two different sites, (1) accompanying a fracking experiment in sedimentary shale at 4~km depth, and (2) above a gas field under depletion. Arrays recordings are compared with recordings available from shallow borehole sensors and examples of detection and location performance of the array are given. The effect of different types of noise at array and borehole stations are compared and discussed.},
  language  = {en}
}
@phdthesis{Nooshiri2020,
  author    = {Nooshiri, Nima},
  title     = {Improvement of routine seismic source parameter estimation based on regional and teleseismic recordings},
  doi       = {10.25932/publishup-45946},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459462},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 118},
  year      = {2020},
  abstract  = {Seismological agencies play an important role in seismological research and seismic hazard mitigation by providing source parameters of seismic events (location, magnitude, mechanism), and keeping these data accessible in the long term. The availability of catalogues of seismic source parameters is an important requirement for the evaluation and mitigation of seismic hazards, and the catalogues are particularly valuable to the research community as they provide fundamental long-term data in the geophysical sciences. This work is well motivated by the rising demand for developing more robust and efficient methods for routine source parameter estimation, and ultimately generation of reliable catalogues of seismic source parameters. Specifically, the aim of this work is to develop some methods to determine hypocentre location and temporal evolution of seismic sources based on regional and teleseismic observations more accurately, and investigate the potential of these methods to be integrated in near real-time processing. To achieve this, a location method that considers several events simultaneously and improves the relative location accuracy among nearby events has been provided. This method tries to reduce the biasing effects of the lateral velocity heterogeneities (or equivalently to compensate for limitations and inaccuracies in the assumed velocity model) by calculating a set of timing corrections for each seismic station. The systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure can be corrected without explicitly solving for a velocity model. Application to sets of multiple earthquakes in complex tectonic environments with strongly heterogeneous structure such as subduction zones and plate boundary region demonstrate that this relocation process significantly improves the hypocentre locations compared to standard locations. To meet the computational demands of this location process, a new open-source software package has been developed that allows for efficient relocation of large-scale multiple seismic events using arrival time data. Upon that, a flexible location framework is provided which can be tailored to various application cases on local, regional, and global scales. The latest version of the software distribution including source codes, a user guide, an example data set, and a change history, is freely available to the community. The developed relocation algorithm has been modified slightly and then its performance in a simulated near real-time processing has been evaluated. It has been demonstrated that applying the proposed technique significantly reduces the bias in routine locations and enhance the ability to locate the lower magnitude events using only regional arrival data. Finally, to return to emphasis on global seismic monitoring, an inversion framework has been developed to determine the seismic source time function through direct waveform fitting of teleseismic recordings. The inversion technique can be systematically applied to moderate- size seismic events and has the potential to be performed in near real-time applications. It is exemplified by application to an abnormal seismic event; the 2017 North Korean nuclear explosion. The presented work and application case studies in this dissertation represent the first step in an effort to establish a framework for automatic, routine generation of reliable catalogues of seismic event locations and source time functions.},
  language  = {en}
}
@phdthesis{Schuck2020,
  author    = {Schuck, Bernhard},
  title     = {Geomechanical and petrological characterisation of exposed slip zones, Alpine Fault, New Zealand},
  doi       = {10.25932/publishup-44612},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-446129},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVII, 143},
  year      = {2020},
  abstract  = {The Alpine Fault is a large, plate-bounding, strike-slip fault extending along the north-western edge of the Southern Alps, South Island, New Zealand. It regularly accommodates large (MW > 8) earthquakes and has a high statistical probability of failure in the near future, i.e., is late in its seismic cycle. This pending earthquake and associated co-seismic landslides are expected to cause severe infrastructural damage that would affect thousands of people, so it presents a substantial geohazard. The interdisciplinary study presented here aims to characterise the fault zone's 4D (space and time) architecture, because this provides information about its rheological properties that will enable better assessment of the hazard the fault poses. The studies undertaken include field investigations of principal slip zone fault gouges exposed along strike of the fault, and subsequent laboratory analyses of these outcrop and additional borehole samples. These observations have provided new information on (I) characteristic microstructures down to the nanoscale that indicate which deformation mechanisms operated within the rocks, (II) mineralogical information that constrains the fault's geomechanical behaviour and (III) geochemical compositional information that allows the influence of fluid- related alteration processes on material properties to be unraveled. Results show that along-strike variations of fault rock properties such as microstructures and mineralogical composition are minor and / or do not substantially influence fault zone architecture. They furthermore provide evidence that the architecture of the fault zone, particularly its fault core, is more complex than previously considered, and also more complex than expected for this sort of mature fault cutting quartzofeldspathic rocks. In particular our results strongly suggest that the fault has more than one principal slip zone, and that these form an anastomosing network extending into the basement below the cover of Quaternary sediments. The observations detailed in this thesis highlight that two major processes, (I) cataclasis and (II) authigenic mineral formation, are the major controls on the rheology of the Alpine Fault. The velocity-weakening behaviour of its fault gouge is favoured by abundant nanoparticles promoting powder lubrication and grain rolling rather than frictional sliding. Wall-rock fragmentation is accompanied by co-seismic, fluid-assisted dilatancy that is recorded by calcite cementation. This mineralisation, along with authigenic formation of phyllosilicates, quickly alters the petrophysical fault zone properties after each rupture, restoring fault competency. Dense networks of anastomosing and mutually cross-cutting calcite veins and intensively reworked gouge matrix demonstrate that strain repeatedly localised within the narrow fault gouge. Abundantly undeformed euhedral chlorite crystallites and calcite veins cross-cutting both fault gouge and gravels that overlie basement on the fault's footwall provide evidence that the processes of authigenic phyllosilicate growth, fluid-assisted dilatancy and associated fault healing are processes active particularly close to the Earth's surface in this fault zone. Exposed Alpine Fault rocks are subject to intense weathering as direct consequence of abundant orogenic rainfall associated with the fault's location at the base of the Southern Alps. Furthermore, fault rock rheology is substantially affected by shallow-depth conditions such as the juxtaposition of competent hanging wall fault rocks on poorly consolidated footwall sediments. This means microstructural, mineralogical and geochemical properties of the exposed fault rocks may differ substantially from those at deeper levels, and thus are not characteristic of the majority of the fault rocks' history. Examples are (I) frictionally weak smectites found within the fault gouges being artefacts formed at temperature conditions, and imparting petrophysical properties that are not typical for most of fault rocks of the Alpine Fault, (II) grain-scale dissolution resulting from subaerial weathering rather than deformation by pressure-solution processes and (III) fault gouge geometries being more complex than expected for deeper counterparts. The methodological approaches deployed in analyses of this, and other fault zones, and the major results of this study are finally discussed in order to contextualize slip zone investigations of fault zones and landslides. Like faults, landslides are major geohazards, which highlights the importance of characterising their geomechanical properties. Similarities between faults, especially those exposed to subaerial processes, and landslides, include mineralogical composition and geomechanical behaviour. Together, this ensures failure occurs predominantly by cataclastic processes, although aseismic creep promoted by weak phyllosilicates is not uncommon. Consequently, the multidisciplinary approach commonly used to investigate fault zones may contribute to increase the understanding of landslide faulting processes and the assessment of their hazard potential.},
  language  = {en}
}
@phdthesis{Maerz2019,
  author    = {Maerz, Sven},
  title     = {Analyzing pore systems through comprehensive digital image analysis (DIA)},
  doi       = {10.25932/publishup-44588},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445880},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 107, xxi},
  year      = {2019},
  abstract  = {Carbonates tend to have complex pore systems which are often composed of distinct assemblages of genetically and geometrically different pore types at various scales (e.g., Melim et al., 2001; Lee et al., 2009; He et al., 2014; Dernaika \& Sinclair, 2017; Zhang et al., 2017). Such carbonate-typical multimodal pore systems are the result of both primary depositional processes and multiple stages of postdepositional modifications, causing small-scale heterogeneities in pore system properties and leading to the co-occurrence of both effective and ineffective pore types. These intrinsic variations in pore type effectiveness are the main reason for the often low correlation between porosity and permeability in carbonate pore systems (e.g., Mazzullo 2004; Ehrenberg \& Nadeau, 2005; Hollis et al., 2010; He et al., 2014; Rashid et al., 2015; Dernaika \& Sinclair, 2017), as it is also true for the marginal lacustrine carbonates studied in this thesis. However, by extracting interconnected and thus effective pore types, and simultaneously excluding isolated and ineffective pores, the understanding and prediction of permeability for given porosity can be highly enhanced (e.g., Melim et al., 2001; Zhang et al., 2017). In this thesis, a step-by-step workflow based on digital image analysis (DIA) is presented and performed on 32 facies-representative samples of marginal lacustrine carbonates from the Middle Miocene N{\"o}rdlinger Ries crater lake (Southern Germany), resulting in 77 mean values of pore type effectiveness which are based on 23,508 individual pore geometry data. By using pore shape factor γ (sensu Anselmetti et al., 1998) as a parameter to quantitatively describe pore shape complexity and therefore pore interconnectivity, the potential contribution (Kcontr.) of each pore type to total permeability (Ktotal) is calculated, and the most effective pore types are then identified. As a result, primary interpeloidal pores and secondary vugs are the most effective pore types in the studied marginal lacustrine succession, mainly due to their generally big size and complex shape, leading to an excellent interconnection between both pore types and consequently to the establishment of a highly effective pore network. Both pore types together compose the pore system of the peloidal grainstone facies. Therefore, this lithofacies type has been identified as the sedimentary facies with highest porosity-permeability properties in this marginal lacustrine succession. By applying the DIA-based method to 23 additional samples from the studied outcrop which all show extensive partial to complete cementation of preexisting pores, the impact of cementation on pore geometry and therefore on porosity and permeability is quantified. This results in a cementation reduction value for each relevant parameter which can then be used to enhance precision of predicting porosity and permeability within the studied succession. Furthermore, the concept of using pore shape complexity as a proxy parameter for pore system effectiveness is tested by applying an independent method (i.e., fluid flow simulation) to the dataset. DIA is then used once again to evaluate the outcome of fluid flow simulation. The results confirm the previous findings that interpeloidal pores and vugs together build up the most effective pore system in the Ries lake carbonates. Finally, the extraction of the interconnected (i.e., effective) pore network leads to an improved correlation between porosity and permeability within the studied carbonates. The step-by-step workflow described in this thesis provides a quantitative petrographic method to identify and extract effective porosity from the pore system, which is crucial for understanding how carbonate pore systems generate permeability. This thesis also demonstrates that pore shape complexity is the most important geometrical parameter controlling pore interconnection and consequently the formation of effective porosity. It further emphasizes that pore shape factor γ (sensu Anselmetti et al. 1998) is a very robust and scale-independent proxy parameter to quantify pore type effectiveness. Additionally, DIA proves to be an ideal tool to directly link porosity and permeability to their mutual origin: the rock fabric and associated pore structure.},
  language  = {de}
}