@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{Wang2011,
  author    = {Wang, Yongbo},
  title     = {Late glacial to Holocene climate and vegetation changes on the Tibetan Plateau inferred from fossil pollen records in lacustrine sediments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-63155},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The past climate in central Asia, and especially on the Tibetan Plateau (TP), is of great importance for an understanding of global climate processes and for predicting the future climate. As a major influence on the climate in this region, the Asian Summer Monsoon (ASM) and its evolutionary history are of vital importance for accurate predictions. However, neither the evolutionary pattern of the summer monsoon nor the driving mechanisms behind it are yet clearly understood. For this research, I first synthesized previously published Late Glacial to Holocene climatic records from monsoonal central Asia in order to extract the general climate signals and the associated summer monsoon intensities. New climate and vegetation sequences were then established using improved quantitative methods, focusing on fossil pollen records recovered from Tibetan lakes and also incorporating new modern datasets. The pollen-vegetation and vegetation-climate relationships on the TP were also evaluated in order to achieve a better understanding of fossil pollen records. The synthesis of previously published moisture-related palaeoclimate records in monsoonal central Asia revealed generally different temporal patterns for the two monsoonal subsystems, i.e. the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM). The ISM appears to have experienced maximum wet conditions during the early Holocene, while many records from the area affected by the EASM indicate relatively dry conditions at that time, particularly in north-central China where the maximum moisture levels occurred during the middle Holocene. A detailed consideration of possible driving factors affecting the summer monsoon, including summer solar insolation and sea surface temperatures, revealed that the ISM was primarily driven by variations in northern hemisphere solar insolation, and that the EASM may have been constrained by the ISM resulting in asynchronous patterns of evolution for these two subsystems. This hypothesis is further supported by modern monsoon indices estimated using the NCEP/NCAR Reanalysis data from the last 50 years, which indicate a significant negative correlation between the two summer monsoon subsystems. By analogy with the early Holocene, intensification of the ISM during coming decades could lead to increased aridification elsewhere as a result of the asynchronous nature of the monsoon subsystems, as can already be observed in the meteorological data from the last 15 years. A quantitative climate reconstruction using fossil pollen records was achieved through analysis of sediment core recovered from Lake Donggi Cona (in the north-eastern part of the TP) which has been dated back to the Last Glacial Maximum (LGM). A new data-set of modern pollen collected from large lakes in arid to semi-arid regions of central Asia is also presented herein. The concept of "pollen source area" was introduced to modern climate calibration based on pollen from large lakes, and was applied to the fossil pollen sequence from Lake Donggi Cona. Extremely dry conditions were found to have dominated the LGM, and a subsequent gradually increasing trend in moisture during the Late Glacial period was terminated by an abrupt reversion to a dry phase that lasted for about 1000 years and coincided with the first Heinrich Event of the northern Atlantic region. Subsequent periods corresponding to the warm B{\o}lling-Aller{\o}d period and the Younger Dryas cold event were followed by moist conditions during the early Holocene, with annual precipitation of up to about 400 mm. A slightly drier trend after 9 cal ka BP was then followed by a second wet phase during the middle Holocene that lasted until 4.5 cal ka BP. Relatively steady conditions with only slight fluctuations then dominated the late Holocene, resulting in the present climatic conditions. In order to investigate the relationship between vegetation and climate, temporal variations in the possible driving factors for vegetation change on the northern TP were examined using a high resolution late Holocene pollen record from Lake Kusai. Moving-window Redundancy Analyses (RDAs) were used to evaluate the correlations between pollen assemblages and individual sedimentary proxies. These analyses have revealed frequent fluctuations in the relative abundances of alpine steppe and alpine desert components, and in particular a decrease in the total vegetation cover at around 1500 cal a BP. The climate was found to have had an important influence on vegetation changes when conditions were relatively wet and stable. However, after the 1500 cal a BP threshold in vegetation cover was crossed the vegetation appears to have been affected more by extreme events such as dust storms or fluvial erosion than by the general climatic trends. In addition, pollen spectra over the last 600 years have been revealed by Procrustes analysis to be significantly different from those recovered from older samples, which is attributed to an increased human impact that resulted in unprecedented changes to the composition of the vegetation. Theoretical models that have been developed and widely applied to the European area (i.e. the Extended R-Value (ERV) model and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model) have been applied to the high alpine TP ecosystems in order to investigate the pollen-vegetation relationships, as well as for quantitative reconstructions of vegetation abundance. The modern pollen-vegetation relationships for four common pollen species on the TP have been investigated using Poaceae as the reference taxa. The ERV Submodel 2 yielded relatively high PPEs for the steppe and desert taxa (Artemisia Chenopodiaceae), and low PPEs for the Cyperaceae that are characteristic of the alpine Kobresia meadows. The plant abundances on the central and north-eastern TP were quantified by applying these PPEs to four post-Late Glacial fossil pollen sequences. The reconstructed vegetation assemblages for the four pollen sequences always yielded smaller compositional species turnovers than suggested by the pollen spectra, indicating that the strength of the previously-reported vegetation changes may therefore have been overestimated. In summary, the key findings of this thesis are that (a) the two ASM subsystems show asynchronous patterns during both the Holocene and modern time periods, (b) fossil pollen records from large lakes reflect regional signals for which the pollen source areas need to be taken into account, (c) climate is not always the main driver for vegetation change, and (d) previously reported vegetation changes on the TP may have been overestimated because they ignored inter-species variations in pollen productivity.},
  language  = {en}
}
@phdthesis{Warkus2002,
  author    = {Warkus, Frank},
  title     = {Die neogene Hebungsgeschichte der Patagonischen Anden im Kontext der Subduktion eines aktiven Spreizungszentrums},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000555},
  school      = {Universit{\"a}t Potsdam},
  year      = {2002},
  abstract  = {Das Ph{\"a}nomen der Subduktion eines aktiven Spreizungszentrums an der S{\"u}dspitze S{\"u}damerikas ist seit langem bekannt. Eine Vielzahl von geologischen Beobachtungen wurden mit diesem Ph{\"a}nomen in Verbindung gebracht, trotzdem ist der genaue Mechanismus der Beeinflussung des aktiven Kontinentalrandes weitgehend unbekannt. Die Zusammenh{\"a}nge zwischen den Subduktionsprozessen und der Entwicklung der patagonischen Anden zwischen 47\&\#176;S und 48\&\#176;S stehen im Mittelpunkt der Untersuchungen. Um eine detaillierte zeitliche Aufl{\"o}sung der zugrunde liegenden Prozesse untersuchen zu k{\"o}nnen, wurde die Entwicklung der Vorlandsedimentation, die thermische Entwicklung und die Heraushebung der Oberkruste des andinen Orogens untersucht und diese in Bezug zur Subduktion des Chile-R{\"u}ckens gesetzt. Im Bereich von 47\&\#176;30\′S wurden die synorogenen Vorlandsedimente der Santa Cruz Formation sedimentologisch untersucht. Diese fluviatilen Sedimente wurden in einem reliefarmen Vorlandgebiet durch h{\"a}ufige Rinnenverlagerung und dem Aufbau von Rinnenumlagerungsg{\"u}rteln in Kombination mit assoziierten großr{\"a}umigen {\"U}berflutungsablagerungen akkumuliert. Sie stehen in einem engen Zusammenhang mit der orogenen Entwicklung im andinen Liefergebiet. Dies spiegelt sich in dem nach oben gr{\"o}ber werdenden Zyklus der Santa Cruz Formation wider. Die magnetostratigraphischen Untersuchungen einer 270 m m{\"a}chtigen Sequenz aus der Basis der Santa Cruz Formation, die mit 329 Einzelproben aus 96 Probenpunkten beprobt wurde, ergab 7 Umkehrungen der geomagnetischen Feldrichtung. Mit Hilfe der geomagnetischen Polarit{\"a}tszeitskala (CANDE AND KENT, 1995) konnte der untersuchte Abschnitt der Santa Cruz Formation zwischen 16.2 und 18.5 Ma datiert werden. Als Tr{\"a}ger der Sedimentations-Remanenz konnten {\"u}berwiegend Pseudoeinbereichs-Magentitpartikel und untergeordnet H{\"a}matitpartikel identifiziert werden. An drei Profilen der Santa Cruz Formation wurden aus Sandsteinlagen unterschiedlicher stratigraphischer Position detritische Apatite mit Hilfe der thermochronologischen Spaltspurmethode untersucht. Die thermisch nicht r{\"u}ckgesetzten, detritischen Apatite spiegeln das Auftreten unterschiedlicher Altersdom{\"a}nen im Liefergebiet der Sedimente wider. In der Kombination mit den geochemischen Gesamtgesteinsuntersuchungen der Sedimente und den petrographischen Untersuchungen der Sandsteine, die ein {\"u}berwiegend andesitisch-vulkanisch gepr{\"a}gtes Liefergebiet widerspiegeln, kann nachgewiesen werden, dass die Erosion im Liefergebiet um 16.5 Ma in tiefere, deformierte Krustensegmente einschneidet. Dies bedeutet, dass aufgrund der Denudation im andinen Orogen erste Sockelgesteinseinheiten in den Bereich der Abtragung gelangen und dass dieser Eintrag um 12 bis 10 Ma ein Volumen einnimmt, das zu signifikanten {\"A}nderungen der Gesamtgesteinsgeochemie der Vorlandsedimente f{\"u}hrt. Die thermochronologische Untersuchung von Apatiten aus rezenten topographischen H{\"o}henprofilen aus der Kernzone der patagonischen Anden im Bereich von 47\&\#176;30\′S zeigen den Beginn einer beschleunigten Heraushebung des Orogens um 7.5 Ma. Aus diesen Untersuchungen kann eine Denudationsrate im Zeitraum der letzen 7 bis 8 Ma von 600 bis 650 m/Ma abgesch{\"a}tzt werden. Die Modellierung der Apatit-Spaltspurergebnisse zeigt eine signifikante Temperaturerh{\"o}hung im Zeitraum zwischen 12 und 8 Ma um 20 bis 30\&\#176;C f{\"u}r diesen Krustenbereich, die mit der Subduktion des aktiven Chile-R{\"u}ckens in diesem Bereich der Anden in Verbindung gebracht wird. Aus den gewonnen Daten kann ein Modell f{\"u}r die Entwicklung der patagonischen Anden seit dem fr{\"u}hen Mioz{\"a}n abgeleitet werden. In diesem Modell wird die orogene Entwicklung in den patagonischen Anden auf eine erh{\"o}hte Konvergenzrate zwischen der Nazca Platte und der S{\"u}damerikanischen Platte zur{\"u}ckgef{\"u}hrt, die f{\"u}r die Heraushebung und Denudation der Anden sowie f{\"u}r die damit verbundene Entwicklung im Vorlandbereich verantwortlich ist. Diese orogene Entwicklung wird in einer sp{\"a}ten Phase durch die nordw{\"a}rts wandernde Subduktion des aktiven Spreizungszentrums des Chile R{\"u}ckens {\"u}berpr{\"a}gt und beeinflusst. Das auf der Integration von geologischen, chronologischen sowie thermochronologischen Daten beruhende Modell kann zahlreiche geologische und geophysikalische Beobachtungen in diesem Bereich der s{\"u}dlichen Anden konsistent erkl{\"a}ren.},
  subject      = {Patagonien ; Neogen ; Hebung ; Subduktion ; Anden},
  language  = {de}
}
@phdthesis{Warkus2001,
  author    = {Warkus, Friederike C.},
  title     = {Untersuchungen an Hochdruckrelikten im zentralen Menderes Massiv, W T{\"u}rkei},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000230},
  school      = {Universit{\"a}t Potsdam},
  year      = {2001},
  abstract  = {Das Menderes Massiv im Westen der T{\"u}rkei stellt eine große Kulmination metamorpher Gesteine dar. Das Untersuchungsgebiet ist im Zentralen Menderes Massiv ({\"O}demis Submassiv) gelegen, das von den beiden aktiven Gr{\"a}ben, dem Gediz Graben im Norden und dem B{\"u}y{\"u}k Menderes Graben im S{\"u}den begrenzt wird. Die Untersuchungen der Eklogit Relikte im zentralen Menderes Massiv haben ergeben, dass sich im Menderes Massiv Hochdruckrelikte in unterschiedlichen tektonischen Positionen befinden. Zum einen existieren Eklogit-Bl{\"o}cke in der obersten Einheit (Selcuk Einheit) des zentralen Menderes Massivs und zum anderen Hochdruck-Relikte in der strukturell mittleren Birgi - Tire Decke. Die Granate der quarzfreien Eklogit-Bl{\"o}cke weisen große {\"A}hnlichkeiten mit denen der HP/LT Gesteine von Sifnos und Syros auf. Die Entwicklung der Eklogit-Bl{\"o}cke in der Olistostrom-Einheit l{\"a}sst sich jedoch nicht mit den Eklogit Relikten in der strukturell mittleren Birgi Tire Decke vergleichen. F{\"u}r die Eklogit-Relikte in der Birgi Tire Decke wurde eine polymetamorphe Entwicklung mithilfe petrologischer Untersuchungen und chemischen und Pb-Pb Datierungen herausgearbeitet. Die Eklogit Relikte geh{\"o}ren zu einem metamorphen Teilpfad, der durch eine Amphibolitfazies 1 - Hochdruck - Amphibolitfazies 2/Granulitfazies charakterisiert ist. Der Endpunkt dieses Teilpfades ist mit Temperaturen zwischen 700 und 750 \&\#176;C und Dr{\"u}cken von 1.2 - 1.4 GPa belegt. F{\"u}r diese Bedingungen konnte ein minimales Alter von 520 Ma durch chemische Datierungen an Monaziten einer Augengneisprobe und Pb-Pb Datierungen an Zirkonen einer Augengneis- und Metagabbroprobe bestimmt werden. Dieser amphibolit/granulitfazieller Endpunkt wird mit den Granitintrusionen des zentralen und s{\"u}dlichen Menderes Massiv korreliert, die in einem Zeitraum zwischen 520 Ma bis 550 Ma stattfanden. Sowohl die Amphibolitfazies 1 als auch das Hochdruckereignis werden der Panafrikanischen Orogenese zugeordnet. F{\"u}r die Hochdruckbedingungen wurden maximale Temperaturen zwischen 680\&\#176;C und 720\&\#176;C und bei einem Druck von 2.2 GPa bestimmt. In den untersuchten Metasedimenten konnte eine prograde metamorphe Entwicklung abgeleitet werden, die amphibolitfazielle Bedingungen von 660\&\#176;C bei 0.6 GPa erreichte. Das Metamorphosealter dieser Metasedimente konnte mit < 100 Ma mittels chemischer Mikrosondendatierung bestimmt werden. Die in den Metasedimenten herausgearbeiteten Druck- und Temperaturbedingungen wurden ebenfalls in den metabasischen Gesteinen bestimmt. Diese Ergebnisse werden als Krustenstapelung der metabasischen Gesteine, Augengneise und Metasedimente interpretiert, die mit der alpinen Orogenese im Zusammenhang stehen. Durch die Ergebnisse dieser Arbeit l{\"a}sst sich die Birgi-Tire Decke im zentralen Menderes Massiv genauer charakterisieren. Sie besteht aus Metasedimenten, pelitischen Gneisen, Augengneisen und metabasichen Gesteinen. Die Gneise (pelitische und Augengneise) und die metabasischen Gesteine stellen panafrikanische Relikte dar, die einen amphibolit- eklogit- amphibolit/granulitfaziellen Metamorphosepfad gespeichert haben. Die amphibolit- bis granulitfazielle Metamorphose h{\"a}ngt mit den Granitintrusionen zusammen und fand in einem Zeitraum zwischen 520 - 550 Ma statt. Große Teile der Metasedimente der Birgi Tire Decke haben jedoch nur eine alpine metamorphe Entwicklung durchlaufen, wo sie unter amphibolitfazielle Bedingungen Krustentiefen erreichten, bei denen sie mit den panafrikanischen Relikten zusammen gestapelt wurden und eine gemeinsame Exhumierung erfahren haben.},
  language  = {de}
}
@phdthesis{Weege2017,
  author    = {Weege, Stefanie},
  title     = {Climatic drivers of retrogressive thaw slump activity and resulting sediment and carbon release to the nearshore zone of Herschel Island, Yukon Territory, Canada},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397947},
  school      = {Universit{\"a}t Potsdam},
  pages     = {163},
  year      = {2017},
  abstract  = {The Yukon Coast in Canada is an ice-rich permafrost coast and highly sensitive to changing environmental conditions. Retrogressive thaw slumps are a common thermoerosion feature along this coast, and develop through the thawing of exposed ice-rich permafrost on slopes and removal of accumulating debris. They contribute large amounts of sediment, including organic carbon and nitrogen, to the nearshore zone. The objective of this study was to 1) identify the climatic and geomorphological drivers of sediment-meltwater release, 2) quantify the amount of released meltwater, sediment, organic carbon and nitrogen, and 3) project the evolution of sediment-meltwater release of retrogressive thaw slumps in a changing future climate. The analysis is based on data collected over 18 days in July 2013 and 18 days in August 2012. A cut-throat flume was set up in the main sediment-meltwater channel of the largest retrogressive thaw slump on Herschel Island. In addition, two weather stations, one on top of the undisturbed tundra and one on the slump floor, measured incoming solar radiation, air temperature, wind speed and precipitation. The discharge volume eroding from the ice-rich permafrost and retreating snowbanks was measured and compared to the meteorological data collected in real time with a resolution of one minute. The results show that the release of sediment-meltwater from thawing of the ice-rich permafrost headwall is strongly related to snowmelt, incoming solar radiation and air temperature. Snowmelt led to seasonal differences, especially due to the additional contribution of water to the eroding sediment-meltwater from headwall ablation, lead to dilution of the sediment-meltwater composition. Incoming solar radiation and air temperature were the main drivers for diurnal and inter-diurnal fluctuations. In July (2013), the retrogressive thaw slump released about 25 000 m³ of sediment-meltwater, containing 225 kg dissolved organic carbon and 2050 t of sediment, which in turn included 33 t organic carbon, and 4 t total nitrogen. In August (2012), just 15 600 m³ of sediment-meltwater was released, since there was no additional contribution from snowmelt. However, even without the additional dilution, 281 kg dissolved organic carbon was released. The sediment concentration was twice as high as in July, with sediment contents of up to 457 g l-1 and 3058 t of sediment, including 53 t organic carbon and 5 t nitrogen, being released. In addition, the data from the 36 days of observations from Slump D were upscaled to cover the main summer season of 1 July to 31 August (62 days) and to include all 229 active retrogressive thaw slumps along the Yukon Coast. In total, all retrogressive thaw slumps along the Yukon Coast contribute a minimum of 1.4 Mio. m³ sediment-meltwater each thawing season, containing a minimum of 172 000 t sediment with 3119 t organic carbon, 327 t nitrogen and 17 t dissolved organic carbon. Therefore, in addition to the coastal erosion input to the Beaufort Sea, retrogressive thaw slumps additionally release 3 \% of sediment and 8 \% of organic carbon into the ocean. Finally, the future evolution of retrogressive thaw slumps under a warming scenario with summer air temperatures increasing by 2-3 °C by 2081-2100, would lead to an increase of 109-114\% in release of sediment-meltwater. It can be concluded that retrogressive thaw slumps are sensitive to climatic conditions and under projected future Arctic warming will contribute larger amounts of thawed permafrost material (including organic carbon and nitrogen) into the environment.},
  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{Wichura2011,
  author    = {Wichura, Henry},
  title     = {Topographic evolution of the East African Plateau : a combined study on lava-flow modeling and paleo-topography},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52363},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The East African Plateau provides a spectacular example of geodynamic plateau uplift, active continental rifting, and associated climatic forcing. It is an integral part of the East African Rift System and has an average elevation of approximately 1,000 m. Its location coincides with a negative Bouguer gravity anomaly with a semi-circular shape, closely related to a mantle plume, which influences the Cenozoic crustal development since its impingement in Eocene-Oligocene time. The uplift of the East African Plateau, preceding volcanism, and rifting formed an important orographic barrier and tectonically controlled environment, which is profoundly influenced by climate driven processes. Its location within the equatorial realm supports recently proposed hypotheses, that topographic changes in this region must be considered as the dominant forcing factor influencing atmospheric circulation patterns and rainfall distribution. The uplift of this region has therefore often been associated with fundamental climatic and environmental changes in East Africa and adjacent regions. While the far-reaching influence of the plateau uplift is widely accepted, the timing and the magnitude of the uplift are ambiguous and are still subject to ongoing discussion. This dilemma stems from the lack of datable, geomorphically meaningful reference horizons that could record surface uplift. In order to quantify the amount of plateau uplift and to find evidence for the existence of significant relief along the East African Plateau prior to rifting, I analyzed and modeled one of the longest terrestrial lava flows; the 300-km-long Yatta phonolite flow in Kenya. This lava flow is 13.5 Ma old and originated in the region that now corresponds to the eastern rift shoulders. The phonolitic flow utilized an old riverbed that once drained the eastern flank of the plateau. Due to differential erosion this lava flow now forms a positive relief above the parallel-flowing Athi River, which is mimicking the course of the paleo-river. My approach is a lava-flow modeling, based on an improved composition and temperature dependent method to parameterize the flow of an arbitrary lava in a rectangular-shaped channel. The essential growth pattern is described by a one-dimensional model, in which Newtonian rheological flow advance is governed by the development of viscosity and/or velocity in the internal parts of the lava-flow front. Comparing assessments of different magma compositions reveal that length-dominated, channelized lava flows are characterized by high effusion rates, rapid emplacement under approximately isothermal conditions, and laminar flow. By integrating the Yatta lava flow dimensions and the covered paleo-topography (slope angle) into the model, I was able to determine the pre-rift topography of the East African Plateau. The modeling results yield a pre-rift slope of at least 0.2°, suggesting that the lava flow must have originated at a minimum elevation of 1,400 m. Hence, high topography in the region of the present-day Kenya Rift must have existed by at least 13.5 Ma. This inferred mid-Miocene uplift coincides with the two-step expansion of grasslands, as well as important radiation and speciation events in tropical Africa. Accordingly, the combination of my results regarding the Yatta lava flow emplacement history, its location, and its morphologic character, validates it as a suitable "paleo-tiltmeter" and has thus to be considered as an important topographic and volcanic feature for the topographic evolution in East Africa.},
  language  = {en}
}
@phdthesis{Wiersberg2001,
  author    = {Wiersberg, Thomas},
  title     = {Edelgase als Tracer f{\"u}r Wechselwirkungen von Krusten- und Mantelfluiden mit diamantf{\"u}hrenden Gesteinen des {\"o}stlichen Baltischen Schildes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000218},
  school      = {Universit{\"a}t Potsdam},
  year      = {2001},
  abstract  = {In der vorliegenden Arbeit werden anhand der Edelgaszusammensetzung von Kimberliten und Lamproiten sowie ihrer gesteinsbildenden Minerale die Wechselwirkungen dieser Gesteine mit Fluiden diskutiert. Die untersuchten Proben stammen vom {\"o}stlichen Baltischen Schild, vom Kola-Kraton (Poria Guba und Kandalaksha) und vom karelischen Kraton (Kostamuksha). Edelgasanalysen nach thermischer oder mechanischer Gasextraktion von 23 Gesamtgesteinsproben und 15 Mineralseparaten ergeben folgendes Bild: Helium- und Neon-Isotopendaten der Fluideinschl{\"u}sse von Lamproiten aus Kostamuksha lassen auf den Einfluss einer fluiden Phase krustaler Herkunft schliessen. Diese Wechselwirkungen fanden wahrscheinlich schon w{\"a}hrend des Magmenaufstiegs statt, denn sp{\"a}tere Einfl{\"u}sse krustaler Fluide auf die Lamproite und ihr Nebengestein (Quarzit) sind gering, wie anhand der C/<sup>36Ar-Zusammensetzung gezeigt wird. Auch sind die mit verschiedenen Datierungsmethoden (Rb-Sr, Sm-Nd, K-Ar) an Mineralseparaten und teilweise an Gesamtgestein ermittelten Alter konsistent und machen eine metamorphe {\"U}berpr{\"a}gung unwahrscheinlich. Aufgrund der Verteilung der primordialen Edelgasisotope zwischen Fluideinschl{\"u}ssen und Gesteinsmatrix ist ein langsamer Magmenaufstieg anzunehmen, was die M{\"o}glichkeit der Kontamination mit einem krustalen Fluid w{\"a}hrend des Magmenaufstiegs erh{\"o}ht. Die Gasextraktion aus Mineralseparaten erfolgte thermisch, wodurch eine Freisetzung der Gase ausschließlich aus Fluideinschl{\"u}ssen nicht m{\"o}glich ist. Hierbei zeigen Amphibol und Klinopyroxen, separiert aus Kostamuksha-Lamproiten, in ihrer Neon-Isotopenzusammensetzung im Vergleich zur krustalen Zusammensetzung (Kennedy et al., 1990) ein leicht erh{\"o}htes Verh{\"a}ltnis von <sup>20Ne/<sup>22Ne, was ein Hinweis auf Mantel-Neon sein k{\"o}nnte. Kalifeldsp{\"a}te, Quarz und Karbonate enthalten dagegen nur Neon krustaler Zusammensetzung. Phlogopite haben sehr kleine Verh{\"a}ltnisse von <sup>20Ne/<sup>22Ne und <sup>21Ne/<sup>22Ne, zur{\"u}ckzuf{\"u}hren auf in-situ-Produktion von <sup>22Ne in Folge von U- und Th-Zerfallsprozessen. Wie unterschiedliche thermische Entgasungsmuster f{\"u}r <sup>40Ar und <sup>36Ar zeigen, ist <sup>36Ar in Fluideinschl{\"u}ssen konzentriert. Das <sup>40Ar/<sup>36Ar-Isotopenverh{\"a}ltnis der Fluideinschl{\"u}sse von Lamproiten aus Kostamuksha ist antikorreliert mit der durch thermische Extraktion bestimmten Gesamtmenge an <sup>36Ar. Argon aus Fluideinschl{\"u}ssen setzt sich daher aus zwei Komponenten zusammen: Einer Komponente mit atmosph{\"a}rischer Argon-Isotopenzusammensetzung und einer krustalen Komponente mit einem Isotopenverh{\"a}ltnis <sup>40Ar/<sup>36Ar > 6000. Diffusion von radiogenem <sup>40Ar aus der Kristallmatrix in die Fluideinschl{\"u}sse spielt keine wesentliche Rolle. Kimberlite aus Poria Guba und Kandalaksha zeigen anhand der Helium- und z. T. auch der Neon-Isotopenzusammensetzung eine Mantelkomponente in den Fluideinschl{\"u}ssen an. Bei einem angenommenen <sup>20Ne/<sup>22Ne-Isotopenverh{\"a}ltnis von 12,5 in der Mantelquelle ergibt sich ein <sup>21Ne/<sup>22Ne-Isotopenverh{\"a}ltnis von 0,073 ± 0,011 sowie ein <sup>3He/<sup>4He-Isotopenverh{\"a}ltnis, welches im Vergleich zum subkontinentalem Mantel (Dunai und Baur, 1995) st{\"a}rker radiogen gepr{\"a}gt ist. Solche Isotopensignaturen sind mit h{\"o}heren Konzentrationen an Uran und Thorium in der Mantelquelle der Kimberlite zu erkl{\"a}ren. Rb-Sr- und Sm-Nd-Altersbestimmungen erfolgten von russischer Seite (Belyatskii et al., 1997; Nikitina et al., 1999) und ergeben ein Alter von 1,23 Ga f{\"u}r den Lamproitvulkanismus in Kostamuksha. Eigene K-Ar-Datierungen an Phlogopiten und Kalifeldsp{\"a}ten stimmen mit einem Alter von 1193 ± 20 Ma fast mit den Rb-Sr- und Sm-Nd-Altern {\"u}berein. Die K-Ar-Datierung an einem Phlogopit aus Poria Guba, separiert aus dem Kimberlit PGK 12a, ergibt ein Alter von 396 Ma, ebenfalls in guter {\"U}bereinstimmung mit Rb-Sr-und Sm-Nd-Altern (ca. 400 Ma, Lokhov, pers. Mitteilung). K-Ar-Altersbestimmungen an Gesamtgestein aus Poria Guba erbrachten kein schl{\"u}ssiges Alter. Die Rb-Sr- und Sm-Nd-Alter des Lamproitmagmatismus in Poria Guba betragen 1,72 Ga (Nikitina et al., 1999). Vergleiche von gemessenen mit berechneten Edelgaskonzentrationen aus in-situ-Produktion zeigen weiterhin, dass in Abh{\"a}ngigkeit vom Alter der Probe Diffusionsprozesse stattgefunden haben, die zu unterschiedlichen und z. T. erheblichen Verlusten an Helium und Neon f{\"u}hrten. Diffusionsverluste an Argon sind dagegen kaum signifikant. Unterschiedliche Diffusionsverluste in Abh{\"a}ngigkeit von Alter und betrachtetem Edelgas zeigen auch die primordialen Edelgase.},
  language  = {de}
}
@phdthesis{Wilke2010,
  author    = {Wilke, Franziska Daniela Helena},
  title     = {Quantifying crystalline exhumation in the Himalaya},
  doi       = {10.25932/publishup-4119},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-43138},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 99},
  year      = {2010},
  abstract  = {In 1915, Alfred Wegener published his hypotheses of plate tectonics that revolutionised the world for geologists. Since then, many scientists have studied the evolution of continents and especially the geologic structure of orogens: the most visible consequence of tectonic processes. Although the morphology and landscape evolution of mountain belts can be observed due to surface processes, the driving force and dynamics at lithosphere scale are less well understood despite the fact that rocks from deeper levels of orogenic belts are in places exposed at the surface. In this thesis, such formerly deeply-buried (ultra-) high-pressure rocks, in particular eclogite facies series, have been studied in order to reveal details about the formation and exhumation conditions and rates and thus provide insights into the geodynamics of the most spectacular orogenic belt in the world: the Himalaya. The specific area investigated was the Kaghan Valley in Pakistan (NW Himalaya). Following closure of the Tethyan Ocean by ca. 55-50 Ma, the northward subduction of the leading edge of India beneath the Eurasian Plate and subsequent collision initiated a long-lived process of intracrustal thrusting that continues today. The continental crust of India - granitic basement, Paleozoic and Mesozoic cover series and Permo-Triassic dykes, sills and lavas - has been buried partly to mantle depths. Today, these rocks crop out as eclogites, amphibolites and gneisses within the Higher Himalayan Crystalline between low-grade metamorphosed rocks (600-640°C/ ca. 5 kbar) of the Lesser Himalaya and Tethyan sediments. Beside tectonically driven exhumation mechanisms the channel flow model, that describes a denudation focused ductile extrusion of low viscosity material developed in the middle to lower crust beneath the Tibetan Plateau, has been postulated. To get insights into the lithospheric and crustal processes that have initiated and driven the exhumation of this (ultra-) high-pressure rocks, mineralogical, petrological and isotope-geochemical investigations have been performed. They provide insights into 1) the depths and temperatures to which these rocks were buried, 2) the pressures and temperatures the rocks have experienced during their exhumation, 3) the timing of these processes 4) and the velocity with which these rocks have been brought back to the surface. In detail, through microscopical studies, the identification of key minerals, microprobe analyses, standard geothermobarometry and modelling using an effective bulk rock composition it has been shown that published exhumation paths are incomplete. In particular, the eclogites of the northern Kaghan Valley were buried to depths of 140-100 km (36-30 kbar) at 790-640°C. Subsequently, cooling during decompression (exhumation) towards 40-35 km (17-10 kbar) and 630-580°C has been superseded by a phase of reheating to about 720-650°C at roughly the same depth before final exhumation has taken place. In the southern-most part of the study area, amphibolite facies assemblages with formation conditions similar to the deduced reheating phase indicate a juxtaposition of both areas after the eclogite facies stage and thus a stacking of Indian Plate units. Radiometric dating of zircon, titanite and rutile by U-Pb and amphibole and micas by Ar-Ar reveal peak pressure conditions at 47-48 Ma. With a maximum exhumation rate of 14 cm/a these rocks reached the crust-mantle boundary at 40-35 km within 1 Ma. Subsequent exhumation (46-41 Ma, 40-35 km) decelerated to ca. 1 mm/a at the base of the continental crust but rose again to about 2 mm/a in the period of 41-31 Ma, equivalent to 35-20 km. Apatite fission track (AFT) and (U-Th)/He ages from eclogites, amphibolites, micaschists and gneisses yielded moderate Oligocene to Miocene cooling rates of about 10°C/Ma in the high altitude northern parts of the Kaghan Valley using the mineral-pair method. AFT ages are of 24.5±3.8 to 15.6±2.1 Ma whereas apatite (U-Th)/He analyses yielded ages between 21.0±0.6 and 5.3±0.2 Ma. The southern-most part of the Valley is dominated by younger late Miocene to Pliocene apatite fission track ages of 7.6±2.1 and 4.0±0.5 Ma that support earlier tectonically and petrologically findings of a juxtaposition and stack of Indian Plate units. As this nappe is tectonically lowermost, a later distinct exhumation and uplift driven by thrusting along the Main Boundary Thrust is inferred. A multi-stage exhumation path is evident from petrological, isotope-geochemical and low temperature thermochronology investigations. Buoyancy driven exhumation caused an initial rapid exhumation: exhumation as fast as recent normal plate movements (ca. 10 cm/a). As the exhuming units reached the crust-mantle boundary the process slowed down due to changes in buoyancy. Most likely, this exhumation pause has initiated the reheating event that is petrologically evident (e.g. glaucophane rimmed by hornblende, ilmenite overgrowth of rutile). Late stage processes involved widespread thrusting and folding with accompanied regional greenschist facies metamorphism, whereby contemporaneous thrusting on the Batal Thrust (seen by some authors equivalent to the MCT) and back sliding of the Kohistan Arc along the inverse reactivated Main Mantle Thrust caused final exposure of these rocks. Similar circumstances have been seen at Tso Morari, Ladakh, India, 200 km further east where comparable rock assemblages occur. In conclusion, as exhumation was already done well before the initiation of the monsoonal system, climate dependent effects (erosion) appear negligible in comparison to far-field tectonic effects.},
  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{Wischnewski2011,
  author    = {Wischnewski, Juliane},
  title     = {Reconstructing climate variability on the Tibetan Plateau : comparing aquatic and terrestrial signals},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52453},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change. Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance. Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments. Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests. The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau.},
  language  = {en}
}
@phdthesis{Witt2018,
  author    = {Witt, Tanja Ivonne},
  title     = {Camera Monitoring at volcanoes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421073},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 140},
  year      = {2018},
  abstract  = {Basaltic fissure eruptions, such as on Hawai'i or on Iceland, are thought to be driven by the lateral propagation of feeder dikes and graben subsidence. Associated solid earth processes, such as deformation and structural development, are well studied by means of geophysical and geodetic technologies. The eruptions themselves, lava fountaining and venting dynamics, in turn, have been much less investigated due to hazardous access, local dimension, fast processes, and resulting poor data availability. This thesis provides a detailed quantitative understanding of the shape and dynamics of lava fountains and the morphological changes at their respective eruption sites. For this purpose, I apply image processing techniques, including drones and fixed installed cameras, to the sequence of frames of video records from two well-known fissure eruptions in Hawai'i and Iceland. This way I extract the dimensions of multiple lava fountains, visible in all frames. By putting these results together and considering the acquisition times of the frames I quantify the variations in height, width and eruption velocity of the lava fountains. Then I analyse these time-series in both time and frequency domains and investigate the similarities and correlations between adjacent lava fountains. Following this procedure, I am able to link the dynamics of the individual lava fountains to physical parameters of the magma transport in the feeder dyke of the fountains. The first case study in this thesis focuses on the March 2011 Pu'u'O'o eruption, Hawai'i, where a continuous pulsating behaviour at all eight lava fountains has been observed. The lava fountains, even those from different parts of the fissure that are closely connected, show a similar frequency content and eruption behaviour. The regular pattern in the heights of lava fountain suggests a controlling process within the magma feeder system like a hydraulic connection in the underlying dyke, affecting or even controlling the pulsating behaviour. The second case study addresses the 2014-2015 Holuhraun fissure eruption, Iceland. In this case, the feeder dyke is highlighted by the surface expressions of graben-like structures and fault systems. At the eruption site, the activity decreases from a continuous line of fire of ~60 vents to a limited number of lava fountains. This can be explained by preferred upwards magma movements through vertical structures of the pre-eruptive morphology. Seismic tremors during the eruption reveal vent opening at the surface and/or pressure changes in the feeder dyke. The evolving topography of the cinder cones during the eruption interacts with the lava fountain behaviour. Local variations in the lava fountain height and width are controlled by the conduit diameter, the depth of the lava pond and the shape of the crater. Modelling of the fountain heights shows that long-term eruption behaviour is controlled mainly by pressure changes in the feeder dyke. This research consists of six chapters with four papers, including two first author and two co-author papers. It establishes a new method to analyse lava fountain dynamics by video monitoring. The comparison with the seismicity, geomorphologic and structural expressions of fissure eruptions shows a complex relationship between focussed flow through dykes, the morphology of the cinder cones, and the lava fountain dynamics at the vents of a fissure eruption.},
  language  = {en}
}
@phdthesis{Wolf2017,
  author    = {Wolf, Julia},
  title     = {Schadenserkennung in Beton durch {\"U}berwachung mit eingebetteten Ultraschallpr{\"u}fk{\"o}pfen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397363},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 142},
  year      = {2017},
  abstract  = {Die zerst{\"o}rungsfreien Pr{\"u}fungen von Bauwerken mit Hilfe von Ultraschallmessverfahren haben in den letzten Jahren an Bedeutung gewonnen. Durch Ultraschallmessungen k{\"o}nnen die Geometrien von Bauteilen bestimmt sowie von außen nicht sichtbare Fehler wie Delaminationen und Kiesnester erkannt werden. Mit neuartigen, in das Betonbauteil eingebetteten Ultraschallpr{\"u}fk{\"o}pfen sollen nun Bauwerke dauerhaft auf Ver{\"a}nderungen {\"u}berpr{\"u}ft werden. Dazu werden Ultraschallsignale direkt im Inneren eines Bauteils erzeugt, was die M{\"o}glichkeiten der herk{\"o}mmlichen Methoden der Bauwerks{\"u}berwachung wesentlich erweitert. Ein Ultraschallverfahren k{\"o}nnte mit eingebetteten Pr{\"u}fk{\"o}pfen ein Betonbauteil kontinuierlich integral {\"u}berwachen und damit auch stetig fortschreitende Gef{\"u}ge{\"a}nderungen, wie beispielsweise Mikrorisse, registrieren. Sicherheitsrelevante Bauteile, die nach dem Einbau f{\"u}r Messungen unzug{\"a}nglich oder mittels Ultraschall, beispielsweise durch zus{\"a}tzliche Beschichtungen der Oberfl{\"a}che, nicht pr{\"u}fbar sind, lassen sich mit eingebetteten Pr{\"u}fk{\"o}pfen {\"u}berwachen. An bereits vorhandenen Bauwerken k{\"o}nnen die Ultraschallpr{\"u}fk{\"o}pfe mithilfe von Bohrl{\"o}chern und speziellem Verpressm{\"o}rtel auch nachtr{\"a}glich in das Bauteil integriert werden. F{\"u}r Fertigbauteile bieten sich eingebettete Pr{\"u}fk{\"o}pfe zur Herstellungskontrolle sowie zur {\"U}berwachung der Baudurchf{\"u}hrung als Werkzeug der Qualit{\"a}tssicherung an. Auch die schnelle Schadensanalyse eines Bauwerks nach Naturkatastrophen, wie beispielsweise einem Erdbeben oder einer Flut, ist denkbar. Durch die gute Ankopplung erm{\"o}glichen diese neuartigen Pr{\"u}fk{\"o}pfe den Einsatz von empfindlichen Auswertungsmethoden, wie die Kreuzkorrelation, die Coda-Wellen-Interferometrie oder die Amplitudenauswertung, f{\"u}r die Signalanalyse. Bei regelm{\"a}ßigen Messungen k{\"o}nnen somit sich anbahnende Sch{\"a}den eines Bauwerks fr{\"u}hzeitig erkannt werden. Da die Sch{\"a}digung eines Bauwerks keine direkt messbare Gr{\"o}ße darstellt, erfordert eine eindeutige Schadenserkennung in der Regel die Messung mehrerer physikalischer Gr{\"o}ßen die geeignet verkn{\"u}pft werden. Physikalische Gr{\"o}ßen k{\"o}nnen sein: Ultraschalllaufzeit, Amplitude des Ultraschallsignals und Umgebungstemperatur. Dazu m{\"u}ssen Korrelationen zwischen dem Zustand des Bauwerks, den Umgebungsbedingungen und den Parametern des gemessenen Ultraschallsignals untersucht werden. In dieser Arbeit werden die neuartigen Pr{\"u}fk{\"o}pfe vorgestellt. Es wird beschrieben, dass sie sich, sowohl in bereits errichtete Betonbauwerke als auch in der Konstruktion befindliche, einbauen lassen. Experimentell wird gezeigt, dass die Pr{\"u}fk{\"o}pfe in mehreren Ebenen eingebettet sein k{\"o}nnen da ihre Abstrahlcharakteristik im Beton nahezu ungerichtet ist. Die Mittenfrequenz von rund 62 kHz erm{\"o}glicht Abst{\"a}nde, je nach Betonart und SRV, von mindestens 3 m zwischen Pr{\"u}fk{\"o}pfen die als Sender und Empf{\"a}nger arbeiten. Die Empfindlichkeit der eingebetteten Pr{\"u}fk{\"o}pfe gegen{\"u}ber Ver{\"a}nderungen im Beton wird an Hand von zwei Laborexperimenten gezeigt, einem Drei-Punkt-Biegeversuch und einem Versuch zur Erzeugung von Frost-Tau-Wechsel Sch{\"a}den. Die Ergebnisse werden mit anderen zerst{\"o}rungsfreien Pr{\"u}fverfahren verglichen. Es zeigt sich, dass die Pr{\"u}fk{\"o}pfe durch die Anwendung empfindlicher Auswertemethoden, auftretende Risse im Beton detektieren, bevor diese eine Gefahr f{\"u}r das Bauwerk darstellen. Abschließend werden Beispiele von Installation der neuartigen Ultraschallpr{\"u}fk{\"o}pfe in realen Bauteilen, zwei Br{\"u}cken und einem Fundament, gezeigt und basierend auf dort gewonnenen ersten Erfahrungen ein Konzept f{\"u}r die Umsetzung einer Langzeit{\"u}berwachung aufgestellt.},
  language  = {de}
}
@phdthesis{Wolf2019,
  author    = {Wolf, Mathias Johannes},
  title     = {The role of partial melting on trace element and isotope systematics of granitic melts},
  doi       = {10.25932/publishup-42370},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423702},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 129},
  year      = {2019},
  abstract  = {Partial melting is a first order process for the chemical differentiation of the crust (Vielzeuf et al., 1990). Redistribution of chemical elements during melt generation crucially influences the composition of the lower and upper crust and provides a mechanism to concentrate and transport chemical elements that may also be of economic interest. Understanding of the diverse processes and their controlling factors is therefore not only of scientific interest but also of high economic importance to cover the demand for rare metals. The redistribution of major and trace elements during partial melting represents a central step for the understanding how granite-bound mineralization develops (Hedenquist and Lowenstern, 1994). The partial melt generation and mobilization of ore elements (e.g. Sn, W, Nb, Ta) into the melt depends on the composition of the sedimentary source and melting conditions. Distinct source rocks have different compositions reflecting their deposition and alteration histories. This specific chemical "memory" results in different mineral assemblages and melting reactions for different protolith compositions during prograde metamorphism (Brown and Fyfe, 1970; Thompson, 1982; Vielzeuf and Holloway, 1988). These factors do not only exert an important influence on the distribution of chemical elements during melt generation, they also influence the volume of melt that is produced, extraction of the melt from its source, and its ascent through the crust (Le Breton and Thompson, 1988). On a larger scale, protolith distribution and chemical alteration (weathering), prograde metamorphism with partial melting, melt extraction, and granite emplacement are ultimately depending on a (plate-)tectonic control (Romer and Kroner, 2016). Comprehension of the individual stages and their interaction is crucial in understanding how granite-related mineralization forms, thereby allowing estimation of the mineralization potential of certain areas. Partial melting also influences the isotope systematics of melt and restite. Radiogenic and stable isotopes of magmatic rocks are commonly used to trace back the source of intrusions or to quantify mixing of magmas from different sources with distinct isotopic signatures (DePaolo and Wasserburg, 1979; Lesher, 1990; Chappell, 1996). These applications are based on the fundamental requirement that the isotopic signature in the melt reflects that of the bulk source from which it is derived. Different minerals in a protolith may have isotopic compositions of radiogenic isotopes that deviate from their whole rock signature (Ayres and Harris, 1997; Knesel and Davidson, 2002). In particular, old minerals with a distinct parent-to-daughter (P/D) ratio are expected to have a specific radiogenic isotope signature. As the partial melting reaction only involves selective phases in a protolith, the isotopic signature of the melt reflects that of the minerals involved in the melting reaction and, therefore, should be different from the bulk source signature. Similar considerations hold true for stable isotopes.},
  language  = {en}
}
@phdthesis{Wolf2002,
  author    = {Wolf, Michael D. C.},
  title     = {Amplituden der Kernphasen im Bereich der Kaustik B und Untersuchung der Struktur der {\"U}bergangszone zum inneren Erdkern mit spektralen Amplituden der diffraktierten Phase PKP(BC)},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000408},
  school      = {Universit{\"a}t Potsdam},
  year      = {2002},
  abstract  = {Das Ziel dieser Arbeit ist es, die Strukturen im {\"a}ußeren Erdkern zu untersuchen und R{\"u}ckschl{\"u}sse auf die sich daraus ergebenden Konsequenzen f{\"u}r geodynamische Modellvorstellungen zu ziehen. Die Untersuchung der Kernphasenkaustik B mit Hilfe einer kumulierten Amplituden-Entfernungskurve ist Gegenstand des ersten Teils. Dazu werden die absoluten Amplituden der PKP-Phasen im Entfernungsbereich von 142 \&\#176; bis 147 \&\#176; bestimmt und mit den Amplituden synthetischer Seismogramme verglichen. Als Datenmaterial dienen die Breitbandregistrierungen des Deutschen Seismologischen Re-gionalnetzes (GRSN 1 ) und des Arrays Gr{\"a}fenberg (GRF). Die verwendeten Wellen-formen werden im WWSSN-SP-Frequenzbereich gefiltert. Als Datenbasis dienen vier Tiefherdbeben der Subduktionszone der Neuen Hebriden (Vanuatu Island) und vier Nuklearexplosionen, die auf dem Mururoa und Fangataufa Atoll im S{\"u}dpazifik stattgefunden haben. Beide Regionen befinden sich vom Regionalnetz aus gesehen in einer Epizentraldistanz von ungef{\"a}hr 145 \&\#176;. Die Verwendung eines homogen instrumentierten Netzes von Detektoren und die Anwendung von Stations- und Magnitudenkorrekturen verringern den Hauptteil der Streuung bei den Amplitudenwerten. Dies gilt auch im Vergleich zu Untersuchungen von langperiodischen Amplituden im Bereich der Kernphasenkaustik (H{\"a}ge, 1981). Ein weiterer Grund f{\"u}r die geringe Streuung ist die ausschließliche Verwendung von Ereignissen mit kurzer impulsiver Herdzeitfunktion. Erst die geringe Streuung der Amplitudenwerte erm{\"o}glicht eine Interpretation der Daten. Die theoretischen Amplitudenkurven der untersuchten Erdmodelle zeigen im Bereich der Kaustik B einen gleichartigen Kurvenverlauf. Bei allen Berechnungen wird ein einheitliches Modell f{\"u}r die G{\"u}te der P- und S-Wellen verwendet, das sich aus den Q-Werten der Modelle CIT112 und PREM 2 zusammensetzt. Die mit diesem Q-Modell berechneten Amplituden liegen in geringem Maße oberhalb der gemessenen Amplituden. Dies braucht nicht ber{\"u}cksichtigt zu werden, da die kumulierte Amplituden-Entfernungskurve anhand der Lage des Maximums auf der Entfernungsachse ausgewertet wird. Folglich wird darauf verzichtet, ein alternatives Q-Modell zu entwickeln. Hinsichtlich der Lage des Kaustikmaximums lassen sich die untersuchten Erdmodelle in zwei Kategorien einteilen. Eine Gruppe besteht aus den Modellen IASP91 und 1066B, deren Maxima bei 144.6 \&\#176; und 144.7 \&\#176; liegen. Zur zweiten Gruppe von Modellen z{\"a}hlen AK135, PREM und SP6 mit den Maxima bei 145.1 \&\#176; und 145.2 \&\#176; (SP6). Die gemessene Amplitudenkurve hat ihr Maximum bei 145 \&\#176;. Alle Entfernungsangaben beziehen sich auf eine Herdtiefe von 200 km. Die Kaustikentfernung f{\"u}r einen Oberfl{\"a}chenherd ist jeweils um 0.454 \&\#176; gr{\"o}ßer als die angegeben Werte. Damit liegen die Maxima der Modelle AK135 und PREM nur 0.1 \&\#176; neben dem der gemessenen kumulierten Amplitudenkurve. Daher wird auf die Erstellung eines eigenen Modells verzichtet, da dieses eine unwesentlich verbesserte Amplitudenkurve aufweisen w{\"u}rde. Das Ergebnis der Untersuchung ist die Erstellung einer gemessenen kumulierten Amplituden-Entfernungskurve f{\"u}r die Kaustik B. Die Kurve legt die Position der Kaustik B f{\"u}r kurzperiodische Daten auf \&\#177; 0.15 \&\#176; fest und bestimmt damit, welche Erdmodelle f{\"u}r die Beschreibung der Amplituden im Entfernungsbereich der Kaustik B besonders geeignet sind. Die Erdmodelle AK135 und PREM, erg{\"a}nzt durch ein einheitliches Q-Modell, geben den Verlauf der Amplituden am besten wieder. Da die Amplitudenkurven beider Modelle nahe beieinander liegen, sind sie als gleichwertig zu bezeichnen. Im zweiten Teil der Arbeit wird die Struktur der {\"U}bergangszone in den inneren Erdkern anhand des spektralen Abklingens der Phase PKP(BC)diff am Punkt C der Laufzeitkurve untersucht. Der physikalische Prozeß der Beugung ist f{\"u}r die starke Abnahme der Amplituden dieser Phase verantwortlich. Die Diffraktion beeinflußt das Abklingverhalten verschiedener Frequenzanteile des seismischen Signals auf unterschiedliche Weise. Eine Deutung des Verhaltens erfordert die Berechnung von Abklingspektren. Dabei wird die Abschw{\"a}chung des PKP(BC)diff Signals f{\"u}r acht Frequenzen zwischen 6.4 s und 1.25 Hz ermittelt und als Spektrum dargestellt. Die Form des Abklingspektrums ist charakteristisch f{\"u}r die Beschaffenheit der Geschwindigkeitsstruktur direkt oberhalb der Grenze zum inneren Erdkern (GIK). Die Beben, deren Kernphasen im Regionalnetz als diffraktierte Kernphasen BCdiff registriert werden, liegen in einem Entfernungsbereich jenseits von 150 \&\#176;. In dieser Distanz befinden sich die Erdbebenherde der Tonga-Fidschi-Subduktionszone, deren Breitbandaufzeichnungen verwendet werden. Die Auswertung unkorrigierter Wellenformen ergibt Abklingspektren, die mit plausiblen Erdmodellen nicht in Einklang zu bringen sind. Aus diesem Grund werden die Daten einer spektralen Stationskorrektur unterzogen, die eigens zu diesem Zweck ermittelt wird. Am Beginn der Auswertung steht eine Pr{\"u}fung bekannter Erdmodelle mit unterschiedlichen Geschwindigkeitsstrukturen oberhalb der GIK. Zu den untersuchten Modellen z{\"a}hlen PREM, IASP91, AK135Q, PREM2, SP6, OICM2 und eine Variante des PREM. Die Untersuchung ergibt, daß Modelle, die einen verringerten Gradienten oberhalb der GIK aufweisen, eine bessere {\"U}bereinstimmung mit den gemessenen Daten zeigen als Modelle ohne diese {\"U}bergangszone. Zur Verifikation dieser These wird ein Erdmodell, das keinen verringerten Gradienten oberhalb der GIK besitzt (PREM), durch eine Reihe unterschiedlicher Geschwindigkeitsverl{\"a}ufe in diesem Bereich erg{\"a}nzt und deren synthetische Seismogramme berechnet. Das Resultat der Untersuchung sind zwei Varianten des PREM, deren Frequenzanalyse eine gute {\"U}bereinstimmung mit den Daten zeigt. Das Abklingspektrum des Erdmodells PD47, das in einer 380 km m{\"a}chtigen Schicht einen negativen Gradienten besitzt, zeigt eine große {\"A}hnlichkeit mit den gemessenen Spektren. Dennoch kann es nicht als realistisches Modell angesehen werden, da der Punkt C in einer zu großen Entfernung liegt. Dar{\"u}ber hinaus m{\"u}ßte die zu kurze Differenzlaufzeit zwischen PKP(AB) und PKP(DF) beziehungsweise PKIKP durch eine gr{\"o}ßere {\"A}nderung der Geschwindigkeitsstruktur im inneren Kern kompensiert werden. Es wird deshalb das Modell PD27a favorisiert, das diese Nachteile nicht aufweist. PD27a besitzt eine Schicht konstanter Geschwindigkeit oberhalb der GIK mit einer M{\"a}chtigkeit von 150 km. Die Art des Geschwindigkeitsverlaufs steht im Einklang mit der geodynamischen Modellvorstellung, nach der eine Anreicherung leichter Elemente oberhalb der GIK vorliegt, die als Ursache f{\"u}r die Konvektion im {\"a}ußeren Erdkern anzusehen ist.},
  language  = {de}
}
@phdthesis{Wolff2011,
  author    = {Wolff, Christian Michael},
  title     = {East African monsoon variability since the last glacial},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58079},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The impact of global warming on human water resources is attracting increasing attention. No other region in this world is so strongly affected by changes in water supply than the tropics. Especially in Africa, the availability and access to water is more crucial to existence (basic livelihoods and economic growth) than anywhere else on Earth. In East Africa, rainfall is mainly influenced by the migration of the Inter-Tropical Convergence Zone (ITCZ) and by the El Ni{\~n}o Southern Oscillation (ENSO) with more rain and floods during El Ni{\~n}o and severe droughts during La Ni{\~n}a. The forecasting of East African rainfall in a warming world requires a better understanding of the response of ENSO-driven variability to mean climate. Unfortunately, existing meteorological data sets are too short or incomplete to establish a precise evaluation of future climate. From Lake Challa near Mount Kilimanjaro, we report records from a laminated lake sediment core spanning the last 25,000 years. Analyzing a monthly cleared sediment trap confirms the annual origin of the laminations and demonstrates that the varve-thicknesses are strongly linked to the duration and strength of the windy season. Given the modern control of seasonal ITCZ location on wind and rain in this region and the inverse relation between the two, thicker varves represent windier and thus drier years. El Ni{\~n}o (La Ni{\~n}a) events are associated with wetter (drier) conditions in east Africa and decreased (increased) surface wind speeds. Based on this fact, the thickness of the varves can be used as a tool to reconstruct a) annual rainfall b) wind season strength, and c) ENSO variability. Within this thesis, I found evidence for centennialscale changes in ENSO-related rainfall variability during the last three millennia, abrupt changes in variability during the Medieval Climate Anomaly and the Little Ice Age, and an overall reduction in East African rainfall and its variability during the Last Glacial period. Climate model simulations support forward extrapolation from these lake-sediment data, indicating that a future Indian Ocean warming will enhance East Africa's hydrological cycle and its interannual variability in rainfall. Furthermore, I compared geochemical analyses from the sediment trap samples with a broad range of limnological, meteorological, and geological parameters to characterize the impact of sedimentation processes from the in-situ rocks to the deposited sediments. As a result an excellent calibration for existing μXRF data from Lake Challa over the entire 25,000 year long profile was provided. The climate development during the last 25,000 years as reconstructed from the Lake Challa sediments is in good agreement with other studies and highlights the complex interactions between long-term orbital forcing, atmosphere, ocean and land surface conditions. My findings help to understand how abrupt climate changes occur and how these changes correlate with climate changes elsewhere on Earth.},
  language  = {en}
}
@phdthesis{Wulf2011,
  author    = {Wulf, Hendrik},
  title     = {Seasonal precipitation, river discharge, and sediment flux in the western Himalaya},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57905},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Rainfall, snow-, and glacial melt throughout the Himalaya control river discharge, which is vital for maintaining agriculture, drinking water and hydropower generation. However, the spatiotemporal contribution of these discharge components to Himalayan rivers is not well understood, mainly because of the scarcity of ground-based observations. Consequently, there is also little known about the triggers and sources of peak sediment flux events, which account for extensive hydropower reservoir filling and turbine abrasion. We therefore lack basic information on the distribution of water resources and controls of erosion processes. In this thesis, I employ various methods to assess and quantify general characteristics of and links between precipitation, river discharge, and sediment flux in the Sutlej Valley. First, I analyze daily precipitation data (1998-2007) from 80 weather stations in the western Himalaya, to decipher the distribution of rain- and snowfall. Rainfall magnitude frequency analyses indicate that 40\% of the summer rainfall budget is attributed to monsoonal rainstorms, which show higher variability in the orogenic interior than in frontal regions. Combined analysis of rainstorms and sediment flux data of a major Sutlej River tributary indicate that monsoonal rainfall has a first order control on erosion processes in the orogenic interior, despite the dominance of snowfall in this region. Second, I examine the contribution of rainfall, snow and glacial melt to river discharge in the Sutlej Valley (s55,000 km2), based on a distributed hydrological model, which covers the period 2000-2008. To achieve high spatial and daily resolution despite limited ground-based observations the hydrological model is forced by daily remote sensing data, which I adjusted and calibrated with ground station data. The calibration shows that the Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall product systematically overestimates rainfall in semi-arid and arid regions, increasing with aridity. The model results indicate that snowmelt-derived discharge (74\%) is most important during the pre-monsoon season (April to June) whereas rainfall (56\%) and glacial melt (17\%) dominate the monsoon season (July-September). Therefore, climate change most likely causes a reduction in river discharge during the pre-monsoon season, which especially affects the orogenic interior. Third, I investigate the controls on suspended sediment flux in different parts of the Sutlej catchments, based on daily gauging data from the past decade. In conjunction with meteorological data, earthquake records, and rock strength measurements I find that rainstorms are the most frequent trigger of high-discharge events with peaks in suspended sediment concentrations (SSC) that account for the bulk of the suspended sediment flux. The suspended sediment flux increases downstream, mainly due to increases in runoff. Pronounced erosion along the Himalayan Front occurs throughout the monsoon season, whereas efficient erosion of the orogenic interior is confined to single extreme events. The results of this thesis highlight the importance of snow and glacially derived melt waters in the western Himalaya, where extensive regions receive only limited amounts of monsoonal rainfall. These regions are therefore particularly susceptible to global warming with major implications on the hydrological cycle. However, the sediment discharge data show that infrequent monsoonal rainstorms that pass the orographic barrier of the Higher Himalaya are still the primary trigger of the highest-impact erosion events, despite being subordinate to snow and glacially-derived discharge. These findings may help to predict peak sediment flux events and could underpin the strategic development of preventative measures for hydropower infrastructures.},
  language  = {en}
}
@phdthesis{Zakharova2015,
  author    = {Zakharova, Olga},
  title     = {Analysis and modeling of transient earthquake patterns and their dependence on local stress regimes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-86455},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 94},
  year      = {2015},
  abstract  = {Investigations in the field of earthquake triggering and associated interactions, which includes aftershock triggering as well as induced seismicity, is important for seismic hazard assessment due to earthquakes destructive power. One of the approaches to study earthquake triggering and their interactions is the use of statistical earthquake models, which are based on knowledge of the basic seismicity properties, in particular, the magnitude distribution and spatiotemporal properties of the triggered events. In my PhD thesis I focus on some specific aspects of aftershock properties, namely, the relative seismic moment release of the aftershocks with respect to the mainshocks; the spatial correlation between aftershock occurrence and fault deformation; and on the influence of aseismic transients on the aftershock parameter estimation. For the analysis of aftershock sequences I choose a statistical approach, in particular, the well known Epidemic Type Aftershock Sequence (ETAS) model, which accounts for the input of background and triggered seismicity. For my specific purposes, I develop two ETAS model modifications in collaboration with Sebastian Hainzl. By means of this approach, I estimate the statistical aftershock parameters and performed simulations of aftershock sequences as well. In the case of seismic moment release of aftershocks, I focus on the ratio of cumulative seismic moment release with respect to the mainshocks. Specifically, I investigate the ratio with respect to the focal mechanism of the mainshock and estimate an effective magnitude, which represents the cumulative aftershock energy (similar to Bath's law, which defines the average difference between mainshock and the largest aftershock magnitudes). Furthermore, I compare the observed seismic moment ratios with the results of the ETAS simulations. In particular, I test a restricted ETAS (RETAS) model which is based on results of a clock advanced model and static stress triggering. To analyze spatial variations of triggering parameters I focus in my second approach on the aftershock occurrence triggered by large mainshocks and the study of the aftershock parameter distribution and their spatial correlation with the coseismic/postseismic slip and interseismic locking. To invert the aftershock parameters I improve the modified ETAS (m-ETAS) model, which is able to take the extension of the mainshock rupture into account. I compare the results obtained by the classical approach with the output of the m-ETAS model. My third approach is concerned with the temporal clustering of seismicity, which might not only be related to earthquake-earthquake interactions, but also to a time-dependent background rate, potentially biasing the parameter estimations. Thus, my coauthors and I also applied a modification of the ETAS model, which is able to take into account time-dependent background activity. It can be applicable for two different cases: when an aftershock catalog has a temporal incompleteness or when the background seismicity rate changes with time, due to presence of aseismic forces. An essential part of any research is the testing of the developed models using observational data sets, which are appropriate for the particular study case. Therefore, in the case of seismic moment release I use the global seismicity catalog. For the spatial distribution of triggering parameters I exploit two aftershock sequences of the Mw8.8 2010 Maule (Chile) and Mw 9.0 2011 Tohoku (Japan) mainshocks. In addition, I use published geodetic slip models of different authors. To test our ability to detect aseismic transients my coauthors and I use the data sets from Western Bohemia (Central Europe) and California. Our results indicate that: (1) the seismic moment of aftershocks with respect to mainshocks depends on the static stress changes and is maximal for the normal, intermediate for thrust and minimal for strike-slip stress regimes, where the RETAS model shows a good correspondence with the results; (2) The spatial distribution of aftershock parameters, obtained by the m-ETAS model, shows anomalous values in areas of reactivated crustal fault systems. In addition, the aftershock density is found to be correlated with coseismic slip gradient, afterslip, interseismic coupling and b-values. Aftershock seismic moment is positively correlated with the areas of maximum coseismic slip and interseismically locked areas. These correlations might be related to the stress level or to material properties variations in space; (3) Ignoring aseismic transient forcing or temporal catalog incompleteness can lead to the significant under- or overestimation of the underlying trigger parameters. In the case when a catalog is complete, this method helps to identify aseismic sources.},
  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{Zamagni2009,
  author    = {Zamagni, Jessica},
  title     = {Responses of a shallow-water ecosystem to the early Paleogene greenhouse environmental conditions : evolution of Larger Foraminifera and coral communities from the Northern Tethys},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-31853},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {Modern anthropogenic forcing of atmospheric chemistry poses the question of how the Earth System will respond as thousands of gigatons of greenhouse gas are rapidly added to the atmosphere. A similar, albeit nonanthropogenic, situation occurred during the early Paleogene, when catastrophic release of carbon to the atmosphere triggered abrupt increase in global temperatures. The best documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar to those expected for the future. This event initiated global warming, changes in hydrological cycles, biotic extinction and migrations. A recently proposed hypothesis concerning changes in marine ecosystems suggests that this global warming strongly influenced the shallow-water biosphere, triggering extinctions and turnover in the Larger Foraminifera (LF) community and the demise of corals. The successions from the Adriatic Carbonate Platform (SW Slovenia) represent an ideal location to test the hypothesis of a possible causal link between the PETM and evolution of shallow-water organisms because they record continuous sedimentation from the Late Paleocene to the Early Eocene and are characterized by a rich biota, especially LF, fundamental for detailed biostratigraphic studies. In order to reconstruct paleoenvironmental conditions during deposition, I focused on sedimentological analysis and paleoecological study of benthic assemblages. During the Late Paleocene-earliest Eocene, sedimentation occurred on a shallow-water carbonate ramp system characterized by enhanced nutrient levels. LF represent the common constituent of the benthic assemblages that thrived in this setting throughout the Late Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic analyses documenting the most complete record to date available for the PETM event in a shallow-water marine environment, I correlated chemostratigraphically for the first time the evolution of LF with the δ¹³C curves. This correlation demonstrated that no major turnover in the LF communities occurred synchronous with the PETM; thus the evolution of LF was mainly controlled by endogenous biotic forces. The study of Late Thanetian metric-sized microbialite-coral mounds which developed in the middle part of the ramp, documented the first Cenozoic occurrence of microbially-cemented mounds. The development of these mounds, with temporary dominance of microbial communities over corals, suggest environmentally-triggered "phase shifts" related to frequent fluctuations of nutrient/turbidity levels during recurrent wet phases which preceding the extreme greenhouse conditions of the PETM. The paleoecological study of the coral community in the microbialites-coral mounds, the study of corals from Early Eocene platform from SW France, and a critical, extensive literature research of Late Paleocene - Early Eocene coral occurrences from the Tethys, the Atlantic, the Caribbean realms suggested that these corals types, even if not forming extensive reefs, are common in the biofacies as small isolated colonies, piles of rubble or small patch-reefs. These corals might have developed 'alternative' life strategies to cope with harsh conditions (high/fluctuating nutrients/turbidity, extreme temperatures, perturbation of aragonite saturation state) during the greenhouse times of the early Paleogene, representing a good fossil analogue to modern corals thriving close to their thresholds for survival. These results demonstrate the complexity of the biological responses to extreme conditions, not only in terms of temperature but also nutrient supply, physical disturbance and their temporal variability and oscillating character.},
  language  = {en}
}
@phdthesis{Zapata2019,
  author    = {Zapata, Sebastian Henao},
  title     = {Paleozoic to Pliocene evolution of the Andean retroarc between 26 and 28°S: interactions between tectonics, climate, and upper plate architecture},
  doi       = {10.25932/publishup-43903},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439036},
  school      = {Universit{\"a}t Potsdam},
  pages     = {139},
  year      = {2019},
  abstract  = {Interactions and feedbacks between tectonics, climate, and upper plate architecture control basin geometry, relief, and depositional systems. The Andes is part of a longlived continental margin characterized by multiple tectonic cycles which have strongly modified the Andean upper plate architecture. In the Andean retroarc, spatiotemporal variations in the structure of the upper plate and tectonic regimes have resulted in marked along-strike variations in basin geometry, stratigraphy, deformational style, and mountain belt morphology. These along-strike variations include high-elevation plateaus (Altiplano and Puna) associated with a thin-skin fold-and-thrust-belt and thick-skin deformation in broken foreland basins such as the Santa Barbara system and the Sierras Pampeanas. At the confluence of the Puna Plateau, the Santa Barbara system and the Sierras Pampeanas, major along-strike changes in upper plate architecture, mountain belt morphology, basement exhumation, and deformation style can be recognized. I have used a source to sink approach to unravel the spatiotemporal tectonic evolution of the Andean retroarc between 26 and 28°S. I obtained a large low-temperature thermochronology data set from basement units which includes apatite fission track, apatite U-Th-Sm/He, and zircon U-Th/He (ZHe) cooling ages. Stratigraphic descriptions of Miocene units were temporally constrained by U-Pb LA-ICP-MS zircon ages from interbedded pyroclastic material. Modeled ZHe ages suggest that the basement of the study area was exhumed during the Famatinian orogeny (550-450 Ma), followed by a period of relative tectonic quiescence during the Paleozoic and the Triassic. The basement experienced horst exhumation during the Cretaceous development of the Salta rift. After initial exhumation, deposition of thick Cretaceous syn-rift strata caused reheating of several basement blocks within the Santa Barbara system. During the Eocene-Oligocene, the Andean compressional setting was responsible for the exhumation of several disconnected basement blocks. These exhumed blocks were separated by areas of low relief, in which humid climate and low erosion rates facilitated the development of etchplains on the crystalline basement. The exhumed basement blocks formed an Eocene to Oligocene broken foreland basin in the back-bulge depozone of the Andean foreland. During the Early Miocene, foreland basin strata filled up the preexisting Paleogene topography. The basement blocks in lower relief positions were reheated; associated geothermal gradients were higher than 25°C/km. Miocene volcanism was responsible for lateral variations on the amount of reheating along the Campo-Arenal basin. Around 12 Ma, a new deformational phase modified the drainage network and fragmented the lacustrine system. As deformation and rock uplift continued, the easily eroded sedimentary cover was efficiently removed and reworked by an ephemeral fluvial system, preventing the development of significant relief. After ~6 Ma, the low erodibility of the basement blocks which began to be exposed caused relief increase, leading to the development of stable fluvial systems. Progressive relief development modified atmospheric circulation, creating a rainfall gradient. After 3 Ma, orographic rainfall and high relief lead to the development of proximal fluvial-gravitational depositional systems in the surrounding basins.},
  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{Zhou2017,
  author    = {Zhou, Bin},
  title     = {On the assessment of surface urban heat island},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404383},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 119},
  year      = {2017},
  abstract  = {Inwiefern St{\"a}dte unter den Megatrends der Urbanisierung und des Klimawandels nachhaltig gestaltet werden k{\"o}nnen, bleibt umstritten. Dies ist zum Teil auf unzureichende Kenntnisse der Mensch-Umwelt-Interaktionen zur{\"u}ckzuf{\"u}hren. Als die am vollst{\"a}ndigsten dokumentierte anthropogene Klimamodifikation ruft der Urbane Hitzeinsel (UHI) Effekt weltweit Sorgen hinsichtlich der Gesundheit der Bev{\"o}lkerung hervor. Dazu kommt noch ein immer h{\"a}ufigeres und intensiveres Auftreten von Hitzewellen, wodurch das Wohlbefinden der Stadtbewohner weiter beeintr{\"a}chtigt wird. Trotz eines deutlichen Anstiegs der Zahl der UHI-bezogenen Ver{\"o}ffentlichungen in den letzten Jahrzehnten haben die unterschiedlichen Definitionen von st{\"a}dtischen und l{\"a}ndlichen Gebieten in bisherigen Studien die allgemeine Vergleichbarkeit der Resultate stark erschwert. Dar{\"u}ber hinaus haben nur wenige Studien den UHI-Effekt und seine Einflussfaktoren anhand einer Kombination der Landnutzungsdaten und der thermischen Fernerkundung systematisch untersucht. Diese Arbeit stellt einen allgemeinen Rahmen zur Quantifizierung von UHI-Intensit{\"a}ten mittels eines automatisierten Algorithmus vor, wobei St{\"a}dte als Agglomerationen maximal r{\"a}umlicher Kontinuit{\"a}t basierend auf Landnutzungsdaten identifiziert, sowie deren l{\"a}ndliche Umfelder analog definiert werden. Durch Verkn{\"u}pfung der Landnutzungsdaten mit Landoberfl{\"a}chentemperaturen von Satelliten kann die UHI-Intensit{\"a}t robust und konsistent berechnet werden. Anhand dieser Innovation wurde nicht nur der Zusammenhang zwischen Stadtgr{\"o}ße und UHI-Intensit{\"a}t erneut untersucht, sondern auch die Auswirkungen der Stadtform auf die UHI-Intensit{\"a}t quantifiziert. Diese Arbeit leistet vielf{\"a}ltige Beitr{\"a}ge zum tieferen Verst{\"a}ndnis des UHI-Ph{\"a}nomens. Erstens wurde eine log-lineare Beziehung zwischen UHI-Intensit{\"a}t und Stadtgr{\"o}ße unter Ber{\"u}cksichtigung der 5,000 europ{\"a}ischen St{\"a}dte best{\"a}tigt. Werden kleinere St{\"a}dte auch ber{\"u}cksichtigt, ergibt sich eine log-logistische Beziehung. Zweitens besteht ein komplexes Zusammenspiel zwischen der Stadtform und der UHI-Intensit{\"a}t: die Stadtgr{\"o}ße stellt den st{\"a}rksten Einfluss auf die UHI-Intensit{\"a}t dar, gefolgt von der fraktalen Dimension und der Anisometrie. Allerdings zeigen ihre relativen Beitr{\"a}ge zur UHI-Intensit{\"a}t eine regionale Heterogenit{\"a}t, welche die Bedeutung r{\"a}umlicher Muster w{\"a}hrend der Umsetzung von UHI-Anpassungsmaßnahmen hervorhebt. Des Weiteren ergibt sich eine neue Saisonalit{\"a}t der UHI-Intensit{\"a}t f{\"u}r individuelle St{\"a}dte in Form von Hysteresekurven, die eine Phasenverschiebung zwischen den Zeitreihen der UHI-Intensit{\"a}t und der Hintergrundtemperatur andeutet. Diese Saisonalit{\"a}t wurde anhand von Luft- und Landoberfl{\"a}chentemperaturen untersucht, indem die Satellitenbeobachtung und die Modellierung der urbanen Grenzschicht mittels des UrbClim-Modells kombiniert wurden. Am Beispiel von London ist die Diskrepanz der Saisonalit{\"a}ten zwischen den beiden Temperaturen vor allem auf die mit der einfallenden Sonnenstrahlung verbundene Besonderheit der Landoberfl{\"a}chentemperatur zur{\"u}ckzuf{\"u}hren. Dar{\"u}ber hinaus spielt das regionale Klima eine wichtige Rolle bei der Entwicklung der UHI. Diese Arbeit ist eine der ersten Studien dieser Art, die eine systematische und statistische Untersuchung des UHI-Effektes erm{\"o}glicht. Die Ergebnisse sind von besonderer Bedeutung f{\"u}r die allgemeine r{\"a}umliche Planung und Regulierung auf Meso- und Makroebenen, damit sich Vorteile der rapiden Urbanisierung nutzbar machen und zeitgleich die folgende Hitzebelastung proaktiv vermindern lassen.},
  language  = {en}
}
@phdthesis{Ziegler2017,
  author    = {Ziegler, Moritz O.},
  title     = {The 3D in-situ stress field and its changes in geothermal reservoirs},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403838},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 110, XV},
  year      = {2017},
  abstract  = {Information on the contemporary in-situ stress state of the earth's crust is essential for geotechnical applications and physics-based seismic hazard assessment. Yet, stress data records for a data point are incomplete and their availability is usually not dense enough to allow conclusive statements. This demands a thorough examination of the in-situ stress field which is achieved by 3D geomechanicalnumerical models. However, the models spatial resolution is limited and the resulting local stress state is subject to large uncertainties that confine the significance of the findings. In addition, temporal variations of the in-situ stress field are naturally or anthropogenically induced. In my thesis I address these challenges in three manuscripts that investigate (1) the current crustal stress field orientation, (2) the 3D geomechanical-numerical modelling of the in-situ stress state, and (3) the phenomenon of injection induced temporal stress tensor rotations. In the first manuscript I present the first comprehensive stress data compilation of Iceland with 495 data records. Therefore, I analysed image logs from 57 boreholes in Iceland for indicators of the orientation of the maximum horizontal stress component. The study is the first stress survey from different kinds of stress indicators in a geologically very young and tectonically active area of an onshore spreading ridge. It reveals a distinct stress field with a depth independent stress orientation even very close to the spreading centre. In the second manuscript I present a calibrated 3D geomechanical-numerical modelling approach of the in-situ stress state of the Bavarian Molasse Basin that investigates the regional (70x70x10km³) and local (10x10x10km³) stress state. To link these two models I develop a multi-stage modelling approach that provides a reliable and efficient method to derive from the larger scale model initial and boundary conditions for the smaller scale model. Furthermore, I quantify the uncertainties in the models results which are inherent to geomechanical-numerical modelling in general and the multi-stage approach in particular. I show that the significance of the models results is mainly reduced due to the uncertainties in the material properties and the low number of available stress magnitude data records for calibration. In the third manuscript I investigate the phenomenon of injection induced temporal stress tensor rotation and its controlling factors. I conduct a sensitivity study with a 3D generic thermo-hydro-mechanical model. I show that the key control factors for the stress tensor rotation are the permeability as the decisive factor, the injection rate, and the initial differential stress. In particular for enhanced geothermal systems with a low permeability large rotations of the stress tensor are indicated. According to these findings the estimation of the initial differential stress in a reservoir is possible provided the permeability is known and the angle of stress rotation is observed. I propose that the stress tensor rotations can be a key factor in terms of the potential for induced seismicity on pre-existing faults due to the reorientation of the stress field that changes the optimal orientation of faults.},
  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{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{Oeztuerk2018,
  author    = {{\"O}zt{\"u}rk, Ugur},
  title     = {Learning more to predict landslides},
  doi       = {10.25932/publishup-42643},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426439},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxi, 104},
  year      = {2018},
  abstract  = {Landslides are frequent natural hazards in rugged terrain, when the resisting frictional force of the surface of rupture yields to the gravitational force. These forces are functions of geological and morphological factors, such as angle of internal friction, local slope gradient or curvature, which remain static over hundreds of years; whereas more dynamic triggering events, such as rainfall and earthquakes, compromise the force balance by temporarily reducing resisting forces or adding transient loads. This thesis investigates landslide distribution and orientation due to landslide triggers (e.g. rainfall) at different scales (6-4∙10^5 km^2) and aims to link rainfall movement with the landslide distribution. It additionally explores the local impacts of the extreme rainstorms on landsliding and the role of precursory stability conditions that could be induced by an earlier trigger, such as an earthquake. Extreme rainfall is a common landslide trigger. Although several studies assessed rainfall intensity and duration to study the distribution of thus triggered landslides, only a few case studies quantified spatial rainfall patterns (i.e. orographic effect). Quantifying the regional trajectories of extreme rainfall could aid predicting landslide prone regions in Japan. To this end, I combined a non-linear correlation metric, namely event synchronization, and radial statistics to assess the general pattern of extreme rainfall tracks over distances of hundreds of kilometers using satellite based rainfall estimates. Results showed that, although the increase in rainfall intensity and duration positively correlates with landslide occurrence, the trajectories of typhoons and frontal storms were insufficient to explain landslide distribution in Japan. Extreme rainfall trajectories inclined northwestwards and were concentrated along some certain locations, such as coastlines of southern Japan, which was unnoticed in the landslide distribution of about 5000 rainfall-triggered landslides. These landslides seemed to respond to the mean annual rainfall rates. Above mentioned findings suggest further investigation on a more local scale to better understand the mechanistic response of landscape to extreme rainfall in terms of landslides. On May 2016 intense rainfall struck southern Germany triggering high waters and landslides. The highest damage was reported at the Braunsbach, which is located on the tributary-mouth fan formed by the Orlacher Bach. Orlacher Bach is a ~3 km long creek that drains a catchment of about ~6 km^2. I visited this catchment in June 2016 and mapped 48 landslides along the creek. Such high landslide activity was not reported in the nearby catchments within ~3300 km^2, despite similar rainfall intensity and duration based on weather radar estimates. My hypothesis was that several landslides were triggered by rainfall-triggered flash floods that undercut hillslope toes along the Orlacher Bach. I found that morphometric features such as slope and curvature play an important role in landslide distribution on this micro scale study site (<10 km^2). In addition, the high number of landslides along the Orlacher Bach could also be boosted by accumulated damages on hillslopes due karst weathering over longer time scales. Precursory damages on hillslopes could also be induced by past triggering events that effect landscape evolution, but this interaction is hard to assess independently from the latest trigger. For example, an earthquake might influence the evolution of a landscape decades long, besides its direct impacts, such as landslides that follow the earthquake. Here I studied the consequences of the 2016 Kumamoto Earthquake (MW 7.1) that triggered some 1500 landslides in an area of ~4000 km^2 in central Kyushu, Japan. Topography, i.e. local slope and curvature, both amplified and attenuated seismic waves, thus controlling the failure mechanism of those landslides (e.g. progressive). I found that topography fails in explaining the distribution and the preferred orientation of the landslides after the earthquake; instead the landslides were concentrated around the northeast of the rupture area and faced mostly normal to the rupture plane. This preferred location of the landslides was dominated mainly by the directivity effect of the strike-slip earthquake, which is the propagation of wave energy along the fault in the rupture direction; whereas amplitude variations of the seismic radiation altered the preferred orientation. I suspect that the earthquake directivity and the asymmetry of seismic radiation damaged hillslopes at those preferred locations increasing landslide susceptibility. Hence a future weak triggering event, e.g. scattered rainfall, could further trigger landslides at those damaged hillslopes.},
  language  = {en}
}