@phdthesis{Schintgen2016, author = {Schintgen, Tom Vincent}, title = {The geothermal potential of Luxembourg}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87110}, school = {Universit{\"a}t Potsdam}, pages = {XXII, 313}, year = {2016}, abstract = {The aim of this work is the evaluation of the geothermal potential of Luxembourg. The approach consists in a joint interpretation of different types of information necessary for a first rather qualitative assessment of deep geothermal reservoirs in Luxembourg and the adjoining regions in the surrounding countries of Belgium, France and Germany. For the identification of geothermal reservoirs by exploration, geological, thermal, hydrogeological and structural data are necessary. Until recently, however, reliable information about the thermal field and the regional geology, and thus about potential geothermal reservoirs, was lacking. Before a proper evaluation of the geothermal potential can be performed, a comprehensive survey of the geology and an assessment of the thermal field are required. As a first step, the geology and basin structure of the Mesozoic Trier-Luxembourg Basin (TLB) is reviewed and updated using recently published information on the geology and structures as well as borehole data available in Luxembourg and the adjoining regions. A Bouguer map is used to get insight in the depth, morphology and structures in the Variscan basement buried beneath the Trier-Luxembourg Basin. The geological section of the old Cessange borehole is reinterpreted and provides, in combination with the available borehole data, consistent information for the production of isopach maps. The latter visualize the synsedimentary evolution of the Trier-Luxembourg Basin. Complementary, basin-wide cross sections illustrate the evolution and structure of the Trier-Luxembourg Basin. The knowledge gained does not support the old concept of the Weilerbach Mulde. The basin-wide cross sections, as well as the structural and sedimentological observations in the Trier-Luxembourg Basin suggest that the latter probably formed above a zone of weakness related to a buried Rotliegend graben. The inferred graben structure designated by SE-Luxembourg Graben (SELG) is located in direct southwestern continuation of the Wittlicher Rotliegend-Senke. The lack of deep boreholes and subsurface temperature prognosis at depth is circumnavigated by using thermal modelling for inferring the geothermal resource at depth. For this approach, profound structural, geological and petrophysical input data are required. Conceptual geological cross sections encompassing the entire crust are constructed and further simplified and extended to lithospheric scale for their utilization as thermal models. The 2-D steady state and conductive models are parameterized by means of measured petrophysical properties including thermal conductivity, radiogenic heat production and density. A surface heat flow of 75 ∓ 7 (2δ) mW m-2 for verification of the thermal models could be determined in the area. The models are further constrained by the geophysically-estimated depth of the lithosphere-asthenosphere boundary (LAB) defined by the 1300 °C isotherm. A LAB depth of 100 km, as seismically derived for the Ardennes, provides the best fit with the measured surface heat flow. The resulting mantle heat flow amounts to ∼40 mW m-2. Modelled temperatures are in the range of 120-125 °C at 5 km depth and of 600-650 °C at the crust/mantle discontinuity (Moho). Possible thermal consequences of the 10-20 Ma old Eifel plume, which apparently caused upwelling of the asthenospheric mantle to 50-60 km depth, were modelled in a steady-state thermal scenario resulting in a surface heat flow of at least 91 mW m-2 (for the plume top at 60 km) in the Eifel region. Available surface heat-flow values are significantly lower (65-80 mW m-2) and indicate that the plume-related heating has not yet entirely reached the surface. Once conceptual geological models are established and the thermal regime is assessed, the geothermal potential of Luxembourg and the surrounding areas is evaluated by additional consideration of the hydrogeology, the stress field and tectonically active regions. On the one hand, low-enthalpy hydrothermal reservoirs in Mesozoic reservoirs in the Trier-Luxembourg Embayment (TLE) are considered. On the other hand, petrothermal reservoirs in the Lower Devonian basement of the Ardennes and Eifel regions are considered for exploitation by Enhanced/Engineered Geothermal Systems (EGS). Among the Mesozoic aquifers, the Buntsandstein aquifer characterized by temperatures of up to 50 °C is a suitable hydrothermal reservoir that may be exploited by means of heat pumps or provide direct heat for various applications. The most promising area is the zone of the SE-Luxembourg Graben. The aquifer is warmest underneath the upper Alzette River valley and the limestone plateau in Lorraine, where the Buntsandstein aquifer lies below a thick Mesozoic cover. At the base of an inferred Rotliegend graben in the same area, temperatures of up to 75 °C are expected. However, geological and hydraulic conditions are uncertain. In the Lower Devonian basement, thick sandstone-/quartzite-rich formations with temperatures >90 °C are expected at depths >3.5 km and likely offer the possibility of direct heat use. The setting of the S{\"u}deifel (South Eifel) region, including the M{\"u}llerthal region near Echternach, as a tectonically active zone may offer the possibility of deep hydrothermal reservoirs in the fractured Lower Devonian basement. Based on the recent findings about the structure of the Trier-Luxembourg Basin, the new concept presents the M{\"u}llerthal-S{\"u}deifel Depression (MSD) as a Cenozoic structure that remains tectonically active and subsiding, and therefore is relevant for geothermal exploration. Beyond direct use of geothermal heat, the expected modest temperatures at 5 km depth (about 120 °C) and increased permeability by EGS in the quartzite-rich Lochkovian could prospectively enable combined geothermal heat production and power generation in Luxembourg and the western realm of the Eifel region.}, language = {en} } @phdthesis{Bora2015, author = {Bora, Sanjay Singh}, title = {Regionally adaptable ground-motion Prediction Equations (GMPEs) for seismic hazard analysis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-88806}, school = {Universit{\"a}t Potsdam}, pages = {xiv, 138}, year = {2015}, abstract = {Adjustment of empirically derived ground motion prediction equations (GMPEs), from a data- rich region/site where they have been derived to a data-poor region/site, is one of the major challenges associated with the current practice of seismic hazard analysis. Due to the fre- quent use in engineering design practices the GMPEs are often derived for response spectral ordinates (e.g., spectral acceleration) of a single degree of freedom (SDOF) oscillator. The functional forms of such GMPEs are based upon the concepts borrowed from the Fourier spectral representation of ground motion. This assumption regarding the validity of Fourier spectral concepts in the response spectral domain can lead to consequences which cannot be explained physically. In this thesis, firstly results from an investigation that explores the relationship between Fourier and response spectra, and implications of this relationship on the adjustment issues of GMPEs, are presented. The relationship between the Fourier and response spectra is explored by using random vibration theory (RVT), a framework that has been extensively used in earthquake engineering, for instance within the stochastic simulation framework and in the site response analysis. For a 5\% damped SDOF oscillator the RVT perspective of response spectra reveals that no one-to-one correspondence exists between Fourier and response spectral ordinates except in a limited range (i.e., below the peak of the response spectra) of oscillator frequencies. The high oscillator frequency response spectral ordinates are dominated by the contributions from the Fourier spectral ordinates that correspond to the frequencies well below a selected oscillator frequency. The peak ground acceleration (PGA) is found to be related with the integral over the entire Fourier spectrum of ground motion which is in contrast to the popularly held perception that PGA is a high-frequency phenomenon of ground motion. This thesis presents a new perspective for developing a response spectral GMPE that takes the relationship between Fourier and response spectra into account. Essentially, this frame- work involves a two-step method for deriving a response spectral GMPE: in the first step two empirical models for the FAS and for a predetermined estimate of duration of ground motion are derived, in the next step, predictions from the two models are combined within the same RVT framework to obtain the response spectral ordinates. In addition to that, a stochastic model based scheme for extrapolating the individual acceleration spectra beyond the useable frequency limits is also presented. To that end, recorded acceleration traces were inverted to obtain the stochastic model parameters that allow making consistent extrapola- tion in individual (acceleration) Fourier spectra. Moreover an empirical model, for a dura- tion measure that is consistent within the RVT framework, is derived. As a next step, an oscillator-frequency-dependent empirical duration model is derived that allows obtaining the most reliable estimates of response spectral ordinates. The framework of deriving the response spectral GMPE presented herein becomes a self-adjusting model with the inclusion of stress parameter (∆σ) and kappa (κ0) as the predictor variables in the two empirical models. The entire analysis of developing the response spectral GMPE is performed on recently compiled RESORCE-2012 database that contains recordings made from Europe, the Mediterranean and the Middle East. The presented GMPE for response spectral ordinates should be considered valid in the magnitude range of 4 ≤ MW ≤ 7.6 at distances ≤ 200 km.}, language = {en} } @phdthesis{Sauma2015, author = {Sauma, Natalia Zamora}, title = {Tsunami hazard analysis in Central America with emphasis on uncertainties}, school = {Universit{\"a}t Potsdam}, pages = {184}, year = {2015}, language = {en} } @phdthesis{Kormann2015, author = {Kormann, Christoph Martin}, title = {Regional climate change effects on hydroclimatic conditions in the Alpine region}, school = {Universit{\"a}t Potsdam}, pages = {129}, year = {2015}, language = {en} } @phdthesis{Kulikova2015, author = {Kulikova, Galina}, title = {Source parameters of the major historical earthquakes in the Tien-Shan region from the late 19th to the early 20th century}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-88370}, school = {Universit{\"a}t Potsdam}, pages = {xiv, 164}, year = {2015}, abstract = {The Tien-Shan and the neighboring Pamir region are two of the largest mountain belts in the world. Their deformation is dominated by intermontane basins bounded by active thrust and reverse faulting. The Tien-Shan mountain belt is characterized by a very high rate of seismicity along its margins as well as within the Tien-Shan interior. The study area of the here presented thesis, the western part of the Tien-Shan region, is currently seismically active with small and moderate sized earthquakes. However, at the end of the 19th beginning of the 20th century, this region was struck by a remarkable series of large magnitude (M>7) earthquakes, two of them reached magnitude 8. Those large earthquakes occurred prior to the installation of the global digital seismic network and therefore were recorded only by analog seismic instruments. The processing of the analog data brings several difficulties, for example, not always the true parameters of the recording system are known. Another complicated task is the digitization of those records - a very time-consuming and delicate part. Therefore a special set of techniques is developed and modern methods are adapted for the digitized instrumental data analysis. The main goal of the presented thesis is to evaluate the impact of large magnitude M≥7.0 earthquakes, which occurred at the turn of 19th to 20th century in the Tien-Shan region, on the overall regional tectonics. A further objective is to investigate the accuracy of previously estimated source parameters for those earthquakes, which were mainly based on macroseismic observations, and re-estimate them based on the instrumental data. An additional aim of this study is to develop the tools and methods for faster and more productive usage of analog seismic data in modern seismology. In this thesis, the ten strongest and most interesting historical earthquakes in Tien-Shan region are analyzed. The methods and tool for digitizing and processing the analog seismic data are presented. The source parameters of the two major M≥8.0 earthquakes in the Northern Tien-Shan are re-estimated in individual case studies. Those studies are published as peer-reviewed scientific articles in reputed journals. Additionally, the Sarez-Pamir earthquake and its connection with one of the largest landslides in the world, Usoy landslide, is investigated by seismic modeling. These results are also published as a research paper. With the developed techniques, the source parameters of seven more major earthquakes in the region are determined and their impact on the regional tectonics was investigated. The large magnitudes of those earthquakes are confirmed by instrumental data. The focal mechanism of these earthquakes were determined providing evidence for responsible faults or fault systems.}, language = {en} } @phdthesis{Kaempf2015, author = {K{\"a}mpf, Lucas}, title = {Extreme events in geoarchives}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85961}, school = {Universit{\"a}t Potsdam}, pages = {xii, 94}, year = {2015}, abstract = {A main limitation in the field of flood hydrology is the short time period covered by instrumental flood time series, rarely exceeding more than 50 to 100 years. However, climate variability acts on short to millennial time scales and identifying causal linkages to extreme hydrological events requires longer datasets. To extend instrumental flood time series back in time, natural geoarchives are increasingly explored as flood recorders. Therefore, annually laminated (varved) lake sediments seem to be the most suitable archives since (i) lake basins act as natural sediment traps in the landscape continuously recording land surface processes including floods and (ii) individual flood events are preserved as detrital layers intercalated in the varved sediment sequence and can be dated with seasonal precision by varve counting. The main goal of this thesis is to improve the understanding about hydrological and sedimentological processes leading to the formation of detrital flood layers and therewith to contribute to an improved interpretation of lake sediments as natural flood archives. This goal was achieved in two ways: first, by comparing detrital layers in sediments of two dissimilar peri-Alpine lakes, Lago Maggiore in Northern Italy and Mondsee in Upper Austria, with local instrumental flood data and, second, by tracking detrital layer formation during floods by a combined hydro-sedimentary monitoring network at Lake Mondsee spanning from the rain fall to the deposition of detrital sediment at the lake floor. Successions of sub-millimetre to 17 mm thick detrital layers were detected in sub-recent lake sediments of the Pallanza Basin in the western part of Lago Maggiore (23 detrital layers) and Lake Mondsee (23 detrital layers) by combining microfacies and high-resolution micro X-ray fluorescence scanning techniques (µ-XRF). The detrital layer records were dated by detailed intra-basin correlation to a previously dated core sequence in Lago Maggiore and varve counting in Mondsee. The intra-basin correlation of detrital layers between five sediment cores in Lago Maggiore and 13 sediment cores in Mondsee allowed distinguishing river runoff events from local erosion. Moreover, characteristic spatial distribution patterns of detrital flood layers revealed different depositional processes in the two dissimilar lakes, underflows in Lago Maggiore as well as under- and interflows in Mondsee. Comparisons with runoff data of the main tributary streams, the Toce River at Lago Maggiore and the Griesler Ache at Mondsee, revealed empirical runoff thresholds above which the deposition of a detrital layer becomes likely. Whereas this threshold is the same for the whole Pallanza Basin in Lago Maggiore (600 m3s-1 daily runoff), it varies within Lake Mondsee. At proximal locations close to the river inflow detrital layer deposition requires floods exceeding a daily runoff of 40 m3s-1, whereas at a location 2 km more distal an hourly runoff of 80 m3s-1 and at least 2 days with runoff above 40 m3s-1 are necessary. A relation between the thickness of individual deposits and runoff amplitude of the triggering events is apparent for both lakes but is obviously further influenced by variable influx and lake internal distribution of detrital sediment. To investigate processes of flood layer formation in lake sediments, hydro-sedimentary dynamics in Lake Mondsee and its main tributary stream, Griesler Ache, were monitored from January 2011 to December 2013. Precipitation, discharge and turbidity were recorded continuously at the rivers outlet to the lake and compared to sediment fluxes trapped close to the lake bottom on a basis of three to twelve days and on a monthly basis in three different water depths at two locations in the lake basin, in a distance of 0.9 (proximal) and 2.8 km (distal) to the Griesler Ache inflow. Within the three-year observation period, 26 river floods of different amplitude (10-110 m3s-1) were recorded resulting in variable sediment fluxes to the lake (4-760 g m-2d-1). Vertical and lateral variations in flood-related sedimentation during the largest floods indicate that interflows are the main processes of lake internal sediment transport in Lake Mondsee. The comparison of hydrological and sedimentological data revealed (i) a rapid sedimentation within three days after the peak runoff in the proximal and within six to ten days in the distal lake basin, (ii) empirical runoff thresholds for triggering sediment flux at the lake floor increasing from the proximal (20 m3s-1) to the distal lake basin (30 m3s-1) and (iii) factors controlling the amount of detrital sediment deposition at a certain location in the lake basin. The total influx of detrital sediment is mainly driven by runoff amplitude, catchment sediment availability and episodic sediment input by local sediment sources. A further role plays the lake internal sediment distribution which is not the same for each event but is favoured by flood duration and the existence of a thermocline and, therewith, the season in which a flood occurred. In summary, the studies reveal a high sensitivity of lake sediments to flood events of different intensity. Certain runoff amplitudes are required to supply enough detrital material to form a visible detrital layer at the lake floor. Reasonable are positive feedback mechanisms between rainfall, runoff, erosion, fluvial sediment transport capacity and lake internal sediment distribution. Therefore, runoff thresholds for detrital layer formation are site-specific due to different lake-catchment characteristics. However, the studies also reveal that flood amplitude is not the only control for the amount of deposited sediment at a certain location in the lake basin even for the strongest flood events. The sediment deposition is rather influenced by a complex interaction of catchment and in-lake processes. This means that the coring location within a lake basin strongly determines the significance of a flood layer record. Moreover, the results show that while lake sediments provide ideal archives for reconstructing flood frequencies, the reconstruction of flood amplitudes is a more complex issue and requires detailed knowledge about relevant catchment and in-lake sediment transport and depositional processes.}, language = {en} } @phdthesis{Ramisch2015, author = {Ramisch, Arne}, title = {Lake system development on the northern Tibetan Plateau during the last ~ 12 ka}, school = {Universit{\"a}t Potsdam}, pages = {122}, year = {2015}, language = {en} } @phdthesis{Zubaidah2010, author = {Zubaidah, Teti}, title = {Spatio-temporal characteristics of the geomagnetic field over the Lombok Island, the Lesser Sunda Islands region}, series = {Scientific Technical Report}, volume = {STR10}, journal = {Scientific Technical Report}, number = {07}, publisher = {Deutsches GeoForschungsZentrum GFZ}, address = {Potsdam}, doi = {10.2312/GFZ.b103-10079}, school = {Universit{\"a}t Potsdam}, pages = {xv, 117}, year = {2010}, abstract = {The Lombok Island is part of the Lesser Sunda Islands (LSI) region - Indonesia, situated along the Sunda-Banda Arcs transition. It lies between zones characterized by the highest intensity geomagnetic anomalies of this region, remarkable as one of the eight most important features provided on the 1st edition of World Digital Magnetic Anomaly Map. The seismicity of this region during the last years is high, while the geological and tectonic structures of this region are still not known in detail. Some local magnetic surveys have been conducted previously during 2004-2005. However, due to the lower accuracy of the used equipment and a limited number of stations, the qualities of the previous measurements are questionable for more interpretations. Thus a more detailed study to better characterize the geomagnetic anomaly -spatially and temporally- over this region and to deeply explore the related regional geology, tectonic and seismicity is needed. The intriguing geomagnetic anomalies over this island region vis-{\`a}-vis the socio-cultural situations lead to a study with a special aim to contribute to the assessment of the potential of natural hazards (earthquakes) as well as a new natural resource of energy (geothermal potential). This study is intended to discuss several crucial questions, including: i. The real values and the general pattern of magnetic anomalies over the island, as well as their relation to the regional one. ii. Any temporal changes of regional anomalies over the recent time. iii. The relationships between the anomalies and the geology and tectonic of this region, especially new insights that can be gained from the geomagnetic observations. iv. The relationships between the anomalies and the high seismicity of this region, especially some possible links between their variations to the earthquake occurrence. First, all available geomagnetic data of this region and results of the previous measurements are evaluated. The new geomagnetic surveys carried out in 2006 and 2007/2008 are then presented in detail, followed by the general description of data processing and data quality evaluation. The new results show the general pattern of contiguous negative-positive anomalies, revealing an active arc related subduction region. They agree with earlier results obtained by satellite, aeromagnetic, and marine platforms; and provide a much more detailed picture of the strong anomalies on this island. The temporal characteristics of regional anomalies show a decreasing strength of the dipolar structure, where decreasing of the field intensities is faster than the regional secular variations as defined by the global model (the 10th generation of IGRF). However, some exceptions (increasing of anomalies) have to be noted and further analyzed for several locations. Thereafter, simultaneous magnetic anomalies and gravity models are generated and interpreted in detail. Three profiles are investigated, providing new insights into the tectonics and geological evolution of the Lombok Island. Geological structure of this island can be divided as two main parts with different consecutive ages: an old part (from late Oligocene to late Miocene) in the South and a younger one (from Pliocene to Holocene) in the North. A new subduction in the back arc region (the Flores Thrust zone) is considered mature and active, showing a tendency of progressive subduction during 2005-2008. Geothermal potential in the northern part of this island can be mapped in more detail using these geomagnetic regional survey data. The earlier estimates of reservoir depth can be confirmed further to a depth of about 800 m. Evaluation of temporal changes of the anomalies gives some possible explanations related to the evolution of the back arc region, large stress accumulations over the LSI region, a specific electrical characteristic of the crust of the Lombok Island region, and a structural discontinuity over this island. Based on the results, several possible advanced studies involving geomagnetic data and anomaly investigations over the Lombok Island region can be suggested for the future: i. Monitoring the subduction activity of the back arc region (the Flores Thrust zone) and the accumulated stress over the LSI, that could contribute to middle term hazard assessment with a special attention to the earthquake occurrence in this region. Continuous geomagnetic field measurements from a geomagnetic observatory which can be established in the northern part of the Lombok Island and systematic measurements at several repeat stations can be useful in this regards. ii. Investigating the specific electrical characteristic (high conductivity) of the crust, that is probably related to some aquifer layers or metal mineralization. It needs other complementary geophysical methods, such as magnetotelluric (MT) or preferably DC resistivity measurements. iii. Determining the existence of an active structural fault over the Lombok Island, that could be related to long term hazard assessment over the LSI region. This needs an extension of geomagnetic investigations over the neighbouring islands (the Bali Island in the West and the Sumbawa Island in the East; probably also the Sumba and the Flores islands). This seems possible because the regional magnetic lineations might be used to delineate some structural discontinuities, based on the modelling of contrasts in crustal magnetizations.}, 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{Kieling2015, author = {Kieling, Katrin}, title = {Quantification of ground motions by broadband simulations}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85989}, school = {Universit{\"a}t Potsdam}, pages = {XIV, 118}, year = {2015}, abstract = {In many procedures of seismic risk mitigation, ground motion simulations are needed to test systems or improve their effectiveness. For example they may be used to estimate the level of ground shaking caused by future earthquakes. Good physical models for ground motion simulation are also thought to be important for hazard assessment, as they could close gaps in the existing datasets. Since the observed ground motion in nature shows a certain variability, part of which cannot be explained by macroscopic parameters such as magnitude or position of an earthquake, it would be desirable that a good physical model is not only able to produce one single seismogram, but also to reveal this natural variability. In this thesis, I develop a method to model realistic ground motions in a way that is computationally simple to handle, permitting multiple scenario simulations. I focus on two aspects of ground motion modelling. First, I use deterministic wave propagation for the whole frequency range - from static deformation to approximately 10 Hz - but account for source variability by implementing self-similar slip distributions and rough fault interfaces. Second, I scale the source spectrum so that the modelled waveforms represent the correct radiated seismic energy. With this scaling I verify whether the energy magnitude is suitable as an explanatory variable, which characterises the amount of energy radiated at high frequencies - the advantage of the energy magnitude being that it can be deduced from observations, even in real-time. Applications of the developed method for the 2008 Wenchuan (China) earthquake, the 2003 Tokachi-Oki (Japan) earthquake and the 1994 Northridge (California, USA) earthquake show that the fine source discretisations combined with the small scale source variability ensure that high frequencies are satisfactorily introduced, justifying the deterministic wave propagation approach even at high frequencies. I demonstrate that the energy magnitude can be used to calibrate the high-frequency content in ground motion simulations. Because deterministic wave propagation is applied to the whole frequency range, the simulation method permits the quantification of the variability in ground motion due to parametric uncertainties in the source description. A large number of scenario simulations for an M=6 earthquake show that the roughness of the source as well as the distribution of fault dislocations have a minor effect on the simulated variability by diminishing directivity effects, while hypocenter location and rupture velocity more strongly influence the variability. The uncertainty in energy magnitude, however, leads to the largest differences of ground motion amplitude between different events, resulting in a variability which is larger than the one observed. For the presented approach, this dissertation shows (i) the verification of the computational correctness of the code, (ii) the ability to reproduce observed ground motions and (iii) the validation of the simulated ground motion variability. Those three steps are essential to evaluate the suitability of the method for means of seismic risk mitigation.}, language = {en} } @phdthesis{Neugebauer2015, author = {Neugebauer, Ina}, title = {Reconstructing climate from the Dead Sea sediment record using high-resolution micro-facies analyses}, series = {Dissertation}, journal = {Dissertation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85266}, school = {Universit{\"a}t Potsdam}, pages = {xiv, 97, XXIII}, year = {2015}, abstract = {The sedimentary record of the Dead Sea is a key archive for reconstructing climate in the eastern Mediterranean region, as it stores the environmental and tectonic history of the Levant for the entire Quaternary. Moreover, the lake is located at the boundary between Mediterranean sub-humid to semi-arid and Saharo-Arabian hyper-arid climates, so that even small shifts in atmospheric circulation are sensitively recorded in the sediments. This DFG-funded doctoral project was carried out within the ICDP Dead Sea Deep Drilling Project (DSDDP) that intended to gain the first long, continuous and high-resolution sediment core from the deep Dead Sea basin. The drilling campaign was performed in winter 2010-11 and more than 700 m of sediments were recovered. The main aim of this thesis was (1) to establish the lithostratigraphic framework for the ~455 m long sediment core from the deep Dead Sea basin and (2) to apply high-resolution micro-facies analyses for reconstructing and better understanding climate variability from the Dead Sea sediments. Addressing the first aim, the sedimentary facies of the ~455 m long deep-basin core 5017-1 were described in great detail and characterised through continuous overview-XRF element scanning and magnetic susceptibility measurements. Three facies groups were classified: (1) the marl facies group, (2) the halite facies group and (3) a group involving different expressions of massive, graded and slumped deposits including coarse clastic detritus. Core 5017-1 encompasses a succession of four main lithological units. Based on first radiocarbon and U-Th ages and correlation of these units to on-shore stratigraphic sections, the record comprises the last ca 220 ka, i.e. the upper part of the Amora Formation (parts of or entire penultimate interglacial and glacial), the last interglacial Samra Fm. (~135-75 ka), the last glacial Lisan Fm. (~75-14 ka) and the Holocene Ze'elim Formation. A major advancement of this record is that, for the first time, also transitional intervals were recovered that are missing in the exposed formations and that can now be studied in great detail. Micro-facies analyses involve a combination of high-resolution microscopic thin section analysis and µXRF element scanning supported by magnetic susceptibility measurements. This approach allows identifying and characterising micro-facies types, detecting event layers and reconstructing past climate variability with up to seasonal resolution, given that the analysed sediments are annually laminated. Within this thesis, micro-facies analyses, supported by further sedimentological and geochemical analyses (grain size, X-ray diffraction, total organic carbon and calcium carbonate contents) and palynology, were applied for two time intervals: (1) The early last glacial period ~117-75 ka was investigated focusing on millennial-scale hydroclimatic variations and lake level changes recorded in the sediments. Thereby, distinguishing six different micro-facies types with distinct geochemical and sedimentological characteristics allowed estimating relative lake level and water balance changes of the lake. Comparison of the results to other records in the Mediterranean region suggests a close link of the hydroclimate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern hemisphere ice sheets during the early last glacial period. (2) A mostly annually laminated late Holocene section (~3700-1700 cal yr BP) was analysed in unprecedented detail through a multi-proxy, inter-site correlation approach of a shallow-water core (DSEn) and its deep-basin counterpart (5017-1). Within this study, a ca 1500 years comprising time series of erosion and dust deposition events was established and anchored to the absolute time-scale through 14C dating and age modelling. A particular focus of this study was the characterisation of two dry periods, from ~3500 to 3300 and from ~3000 to 2400 cal yr BP, respectively. Thereby, a major outcome was the coincidence of the latter dry period with a period of moist and cold climate in Europe related to a Grand Solar Minimum around 2800 cal yr BP and an increase in flood events despite overall dry conditions in the Dead Sea region during that time. These contrasting climate signatures in Europe and at the Dead Sea were likely linked through complex teleconnections of atmospheric circulation, causing a change in synoptic weather patterns in the eastern Mediterranean. In summary, within this doctorate the lithostratigraphic framework of a unique long sediment core from the deep Dead Sea basin is established, which serves as a base for any further high-resolution investigations on this core. It is demonstrated in two case studies that micro-facies analyses are an invaluable tool to understand the depositional processes in the Dead Sea and to decipher past climate variability in the Levant on millennial to seasonal time-scales. Hence, this work adds important knowledge helping to establish the deep Dead Sea record as a key climate archive of supra-regional significance.}, language = {en} } @phdthesis{Hunke2015, author = {Hunke, Philip Paul}, title = {The Brazilian Cerrado: ecohydrological assessment of water and soil degradation in heavily modified meso-scale catchments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85110}, school = {Universit{\"a}t Potsdam}, pages = {xi, 124}, year = {2015}, abstract = {The Brazilian Cerrado is recognised as one of the most threatened biomes in the world, as the region has experienced a striking change from natural vegetation to intense cash crop production. The impacts of rapid agricultural expansion on soil and water resources are still poorly understood in the region. Therefore, the overall aim of the thesis is to improve our understanding of the ecohydrological processes causing water and soil degradation in the Brazilian Cerrado. I first present a metaanalysis to provide quantitative evidence and identifying the main impacts of soil and water alterations resulting from land use change. Second, field studies were conducted to (i) examine the effects of land use change on soils of natural cerrado transformed to common croplands and pasture and (ii) indicate how agricultural production affects water quality across a meso-scale catchment. Third, the ecohydrological process-based model SWAT was tested with simple scenario analyses to gain insight into the impacts of land use and climate change on the water cycling in the upper S{\~a}o Louren{\c{c}}o catchment which experienced decreasing discharges in the last 40 years. Soil and water quality parameters from different land uses were extracted from 89 soil and 18 water studies in different regions across the Cerrado. Significant effects on pH, bulk density and available P and K for croplands and less-pronounced effects on pastures were evident. Soil total N did not differ between land uses because most of the cropland sites were N-fixing soybean cultivations, which are not artificially fertilized with N. By contrast, water quality studies showed N enrichment in agricultural catchments, indicating fertilizer impacts and potential susceptibility to eutrophication. Regardless of the land use, P is widely absent because of the high-fixing capacities of deeply weathered soils and the filtering capacity of riparian vegetation. Pesticides, however, were consistently detected throughout the entire aquatic system. In several case studies, extremely high-peak concentrations exceeded Brazilian and EU water quality limits, which pose serious health risks. My field study revealed that land conversion caused a significant reduction in infiltration rates near the soil surface of pasture (-96 \%) and croplands (-90 \% to -93 \%). Soil aggregate stability was significantly reduced in croplands than in cerrado and pasture. Soybean crops had extremely high extractable P (80 mg kg-1), whereas pasture N levels declined. A snapshot water sampling showed strong seasonality in water quality parameters. Higher temperature, oxi-reduction potential (ORP), NO2-, and very low oxygen concentrations (<5 mg•l-1) and saturation (<60 \%) were recorded during the rainy season. By contrast, remarkably high PO43- concentrations (up to 0.8 mg•l-1) were measured during the dry season. Water quality parameters were affected by agricultural activities at all sampled sub-catchments across the catchment, regardless of stream characteristic. Direct NO3- leaching appeared to play a minor role; however, water quality is affected by topsoil fertiliser inputs with impact on small low order streams and larger rivers. Land conversion leaving cropland soils more susceptible to surface erosion by increased overland flow events. In a third study, the field data were used to parameterise SWAT. The model was tested with different input data and calibrated in SWAT-CUP using the SUFI-2 algorithm. The model was judged reliable to simulate the water balance in the Cerrado. A complete cerrado, pasture and cropland cover was used to analyse the impact of land use on water cycling as well as climate change projections (2039-2058) according to the projections of the RCP 8.5 scenario. The actual evapotranspiration (ET) for the cropland scenario was higher compared to the cerrado cover (+100 mm a-1). Land use change scenarios confirmed that deforestation caused higher annual ET rates explaining partly the trend of decreased streamflow. Taking all climate change scenarios into account, the most likely effect is a prolongation of the dry season (by about one month), with higher peak flows in the rainy season. Consequently, potential threats for crop production with lower soil moisture and increased erosion and sediment transport during the rainy season are likely and should be considered in adaption plans. From the three studies of the thesis I conclude that land use intensification is likely to seriously limit the Cerrado's future regarding both agricultural productivity and ecosystem stability. Because only limited data are available for the vast biome, we recommend further field studies to understand the interaction between terrestrial and aquatic systems. This thesis may serve as a valuable database for integrated modelling to investigate the impact of land use and climate change on soil and water resources and to test and develop mitigation measures for the Cerrado in the future.}, language = {en} } @phdthesis{Allroggen2015, author = {Allroggen, Niklas}, title = {Observation of subsurface flow from the surface : applications of ground-penetrating radar}, school = {Universit{\"a}t Potsdam}, pages = {67}, year = {2015}, language = {en} } @phdthesis{TorresAcosta2015, author = {Torres Acosta, Ver{\´o}nica}, title = {Denudation processes in a tectonically active rift on different time scales}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-84534}, school = {Universit{\"a}t Potsdam}, pages = {xv, ix, 183}, year = {2015}, abstract = {Continental rifts are excellent regions where the interplay between extension, the build-up of topography, erosion and sedimentation can be evaluated in the context of landscape evolution. Rift basins also constitute important archives that potentially record the evolution and migration of species and the change of sedimentary conditions as a result of climatic change. Finally, rifts have increasingly become targets of resource exploration, such as hydrocarbons or geothermal systems. The study of extensional processes and the factors that further modify the mainly climate-driven surface process regime helps to identify changes in past and present tectonic and geomorphic processes that are ultimately recorded in rift landscapes. The Cenozoic East African Rift System (EARS) is an exemplary continental rift system and ideal natural laboratory to observe such interactions. The eastern and western branches of the EARS constitute first-order tectonic and topographic features in East Africa, which exert a profound influence on the evolution of topography, the distribution and amount of rainfall, and thus the efficiency of surface processes. The Kenya Rift is an integral part of the eastern branch of the EARS and is characterized by high-relief rift escarpments bounded by normal faults, gently tilted rift shoulders, and volcanic centers along the rift axis. Considering the Cenozoic tectonic processes in the Kenya Rift, the tectonically controlled cooling history of rift shoulders, the subsidence history of rift basins, and the sedimentation along and across the rift, may help to elucidate the morphotectonic evolution of this extensional province. While tectonic forcing of surface processes may play a minor role in the low-strain rift on centennial to millennial timescales, it may be hypothesized that erosion and sedimentation processes impacted by climate shifts associated with pronounced changes in the availability in moisture may have left important imprints in the landscape. In this thesis I combined thermochronological, geomorphic field observations, and morphometry of digital elevation models to reconstruct exhumation processes and erosion rates, as well as the effects of climate on the erosion processes in different sectors of the rift. I present three sets of results: (1) new thermochronological data from the northern and central parts of the rift to quantitatively constrain the Tertiary exhumation and thermal evolution of the Kenya Rift. (2) 10Be-derived catchment-wide mean denudation rates from the northern, central and southern rift that characterize erosional processes on millennial to present-day timescales; and (3) paleo-denudation rates in the northern rift to constrain climatically controlled shifts in paleoenvironmental conditions during the early Holocene (African Humid Period). Taken together, my studies show that time-temperature histories derived from apatite fission track (AFT) analysis, zircon (U-Th)/He dating, and thermal modeling bracket the onset of rifting in the Kenya Rift between 65-50 Ma and about 15 Ma to the present. These two episodes are marked by rapid exhumation and, uplift of the rift shoulders. Between 45 and 15 Ma the margins of the rift experienced very slow erosion/exhumation, with the accommodation of sediments in the rift basin. In addition, I determined that present-day denudation rates in sparsely vegetated parts of the Kenya Rift amount to 0.13 mm/yr, whereas denudation rates in humid and more densely vegetated sectors of the rift flanks reach a maximum of 0.08 mm/yr, despite steeper hillslopes. I inferred that hillslope gradient and vegetation cover control most of the variation in denudation rates across the Kenya Rift today. Importantly, my results support the notion that vegetation cover plays a fundamental role in determining the voracity of erosion of hillslopes through its stabilizing effects on the land surface. Finally, in a pilot study I highlighted how paleo-denudation rates in climatic threshold areas changed significantly during times of transient hydrologic conditions and involved a sixfold increase in erosion rates during increased humidity. This assessment is based on cosmogenic nuclide (10Be) dating of quartzitic deltaic sands that were deposited in the northern Kenya Rift during a highstand of Lake Suguta, which was associated with the Holocene African Humid Period. Taken together, my new results document the role of climate variability in erosion processes that impact climatic threshold environments, which may provide a template for potential future impacts of climate-driven changes in surface processes in the course of Global Change.}, language = {en} } @phdthesis{Kuetter2015, author = {K{\"u}tter, Sissy}, title = {Magnetotelluric measurements across the southern Barberton Greenstone Belt, South Africa}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-83198}, school = {Universit{\"a}t Potsdam}, pages = {xix, 156}, year = {2015}, abstract = {Der Barberton Gr{\"u}nsteing{\"u}rtel (BGB) in S{\"u}dafrika geh{\"o}rt zu den wenigen Regionen mit noch gut erhaltener Archaischer Kruste. Seit Jahrhunderten wurde der BGB eingehend untersucht und seine geologischen und tektonischen Strukturen detailliert kartiert. {\"U}ber die tiefere Struktur des BGB ist hingegen wenig bekannt. Zahlreiche Evolutionsmodelle, die auf Altersbestimmungsdaten und strukturellen Informationen beruhen wurden {\"u}ber die Jahre aufgestellt. Diese Theorien sind zumeist widerspr{\"u}chlich. Sie konzentrieren sich im Wesentlichen auf die Frage, ob plattentektonische Prozesse bereits bei der Entwicklung der fr{\"u}hen Erde eine Rolle spielten oder ob vertikale Tektonik, angetrieben durch die im Archaikum h{\"o}heren Temperaturen, die Bildung der heutigen Kontinente bestimmt hat. Um neue Erkenntnisse {\"u}ber die interne Struktur und Entwicklungsgeschichte des BGB zu erhalten, wurden im Rahmen der Deutsch-S{\"u}dafrikanischen Forschungsinitiative Inkaba yeAfrica magnetotellurische (MT) Messungen durchgef{\"u}hrt. Entlang von sechs Profilen, die den gesamten s{\"u}dlichen Teil des BGB's {\"u}berdecken, wurden nahezu 200 MT-Stationen installiert. Tektonische Strukturen wie z. B. (fossile) Verwerfungszonen k{\"o}nnen erh{\"o}hte Leitf{\"a}higigkeiten haben, wenn sich leitf{\"a}hige Mineralisationen innerhalb der Scherzonen gebildet haben. Durch die Abbildung der elektrischen Leitf{\"a}higkeitsverteilung des Untergrundes mit Hilfe von MT Messungen kann der Verlauf tektonischer Strukturen nachvollzogen werden, woraus Schl{\"u}sse {\"u}ber m{\"o}glicherweise abgelaufene tektonische Prozesse gezogen werden k{\"o}nnen. Der gesamte MT Datensatz weist starke St{\"o}reinfl{\"u}sse durch k{\"u}nstliche elektromagnetische Signale auf, die bspw. von Stromleitungen und elektrischen Z{\"a}unen stammen. Insbesondere langperiodische Daten (>1 s) sind davon betroffen, die f{\"u}r die Aufl{\"o}sung tieferer Strukturen notwendig sind. Die Anwendung etablierter Ans{\"a}tze wie Verschiebungsfiltern und der Remote Reference-Methode, f{\"u}hrte zu Verbesserungen vorrangig f{\"u}r Perioden < 1 s. Der langperiodische Bereich ist durch impulsartige St{\"o}rsignale in den magnetischen und dazugeh{\"o}rigen Stufen in den elektrischen Feldkomponenten gepr{\"a}gt. Im Rahmen dieser Arbeit wurde ein neuartiger Zeitbereichs-Filter entwickelt, welcher auf einer abgewandelten Form des Wiener Filters beruht und diese Art von St{\"o}rsignalen aus den Daten entfernt. Durch den Vergleich der Datenvarianz einer lokalen Station mit der einer Referenzstation k{\"o}nnen gest{\"o}rte Zeitsegmente identifiziert werden. Anschließend wird ein Wiener-Filter-Algorithmus angewendet, um f{\"u}r diese Segmente mithilfe der Referenzdaten physikalisch sinnvolle Zeitreihen zu berechnen, mit denen die Daten der lokalen Station ersetzt werden. W{\"a}hrend impulsartige St{\"o}rsignale in den magnetischen Datenkan{\"a}len relativ einfach erfasst werden k{\"o}nnen, ist die Detektion von Vers{\"a}tzen in den elektrischen Zeitreihen je nach Versatzh{\"o}he problematischer. Um dieses Problem zu umgehen, habe ich einen Algorithmus entwickelt, bei dem die Zeitreihen differenziert, gefiltert und im letzten Schritt integriert werden. In einer zweiten von mir entwickelten Filtermethode werden die St{\"o}rsignale durch den Vergleich des kurzzeitigen und des langzeitigen Datenmittelwerts ausfindig gemacht. Bei diesem Filter werden die St{\"o}rsignale aus den Zeitreihen entfernt und durch eine lineare Interpolation ersetzt. Durch die beiden Filtermethoden wurde eine deutliche Verbesserung der Datenqualit{\"a}t bis zu 10 und teilweise 100 s erreicht. Zur Interpretation des MT-Datensatzes wurden 2D und 3D Inversionen durchgef{\"u}hrt. Die so erhaltenen elektrischen Leitf{\"a}higkeitsmodelle zeigen eine gute {\"U}bereinstimmung mit den kartierten, geologischen Strukturen. Die Gesteine des BGB weisen in den Modellen hohe Widerst{\"a}nde auf und sind deutlich von leitf{\"a}higen benachbarten geologischen Strukturen abgegrenzt. Verwerfungszonen korrelieren mit leitf{\"a}higen Strukturen, die sich bis in eine Tiefe von 5 bis 10 km erstrecken. Eine Fortsetzung der Verwerfungszonen {\"u}ber die s{\"u}dliche Grenze des BGB wird in den 2D-Ergebnissen angedeutet. Insgesamt zeigen die Inversionsmodelle, dass vermutlich sowohl plattentektonische als auch vertikaltektonische Prozesse bei der Entstehung des BGB eine wichtige Rolle spielten.}, language = {en} } @phdthesis{Brosinsky2015, author = {Brosinsky, Arlena}, title = {Spectral fingerprinting}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-83369}, school = {Universit{\"a}t Potsdam}, pages = {VI, 117}, year = {2015}, abstract = {Current research on runoff and erosion processes, as well as an increasing demand for sustainable watershed management emphasize the need for an improved understanding of sediment dynamics. This involves the accurate assessment of erosion rates and sediment transfer, yield and origin. A variety of methods exist to capture these processes at the catchment scale. Among these, sediment fingerprinting, a technique to trace back the origin of sediment, has attracted increasing attention by the scientific community in recent years. It is a two-step procedure, based on the fundamental assumptions that potential sources of sediment can be reliably discriminated based on a set of characteristic 'fingerprint' properties, and that a comparison of source and sediment fingerprints allows to quantify the relative contribution of each source. This thesis aims at further assessing the potential of spectroscopy to assist and improve the sediment fingerprinting technique. Specifically, this work focuses on (1) whether potential sediment sources can be reliably identified based on spectral features ('fingerprints'), whether (2) these spectral fingerprints permit the quantification of relative source contribution, and whether (3) in situ derived source information is sufficient for this purpose. Furthermore, sediment fingerprinting using spectral information is applied in a study catchment to (4) identify major sources and observe how relative source contributions change between and within individual flood events. And finally, (5) spectral fingerprinting results are compared and combined with simultaneous sediment flux measurements to study sediment origin, transport and storage behaviour. For the sediment fingerprinting approach, soil samples were collected from potential sediment sources within the Is{\´a}bena catchment, a meso-scale basin in the central Spanish Pyrenees. Undisturbed samples of the upper soil layer were measured in situ using an ASD spectroradiometer and subsequently sampled for measurements in the laboratory. Suspended sediment was sampled automatically by means of ISCO samplers at the catchment as well as at the five major subcatchment outlets during flood events, and stored fine sediment from the channel bed was collected from 14 cross-sections along the main river. Artificial mixtures of known contributions were produced from source soil samples. Then, all source, sediment and mixture samples were dried and spectrally measured in the laboratory. Subsequently, colour coefficients and physically based features with relation to organic carbon, iron oxide, clay content and carbonate, were calculated from all in situ and laboratory spectra. Spectral parameters passing a number of prerequisite tests were submitted to principal component analyses to study natural clustering of samples, discriminant function analyses to observe source differentiation accuracy, and a mixing model for source contribution assessment. In addition, annual as well as flood event based suspended sediment fluxes from the catchment and its subcatchments were calculated from rainfall, water discharge and suspended sediment concentration measurements using rating curves and Quantile Regression Forests. Results of sediment flux monitoring were interpreted individually with respect to storage behaviour, compared to fingerprinting source ascriptions and combined with fingerprinting to assess their joint explanatory potential. In response to the key questions of this work, (1) three source types (land use) and five spatial sources (subcatchments) could be reliably discriminated based on spectral fingerprints. The artificial mixture experiment revealed that while (2) laboratory parameters permitted source contribution assessment, (3) the use of in situ derived information was insufficient. Apparently, high discrimination accuracy does not necessarily imply good quantification results. When applied to suspended sediment samples of the catchment outlet, the spectral fingerprinting approach was able to (4) quantify the major sediment sources: badlands and the Villacarli subcatchment, respectively, were identified as main contributors, which is consistent with field observations and previous studies. Thereby, source contribution was found to vary both, within and between individual flood events. Also sediment flux was found to vary considerably, annually as well as seasonally and on flood event base. Storage was confirmed to play an important role in the sediment dynamics of the studied catchment, whereas floods with lower total sediment yield tend to deposit and floods with higher yield rather remove material from the channel bed. Finally, a comparison of flux measurements with fingerprinting results highlighted the fact that (5) immediate transport from sources to the catchment outlet cannot be assumed. A combination of the two methods revealed different aspects of sediment dynamics that none of the techniques could have uncovered individually. In summary, spectral properties provide a fast, non-destructive, and cost-efficient means to discriminate and quantify sediment sources, whereas, unfortunately, straight-forward in situ collected source information is insufficient for the approach. Mixture modelling using artificial mixtures permits valuable insights into the capabilities and limitations of the method and similar experiments are strongly recommended to be performed in the future. Furthermore, a combination of techniques such as e.g. (spectral) sediment fingerprinting and sediment flux monitoring can provide comprehensive understanding of sediment dynamics.}, language = {en} } @phdthesis{Abon2015, author = {Abon, Catherine Cristobal}, title = {Radar-based rainfall retrieval for flood forecasting in a meso-scale catchment}, school = {Universit{\"a}t Potsdam}, pages = {93 S.}, year = {2015}, language = {en} } @article{VormoorLawrenceHeistermannetal.2015, author = {Vormoor, Klaus Josef and Lawrence, D. and Heistermann, Maik and Bronstert, Axel}, title = {Climate change impacts on the seasonality and generation processes of floods}, series = {Hydrology and earth system sciences : HESS}, volume = {19}, journal = {Hydrology and earth system sciences : HESS}, number = {2}, publisher = {Copernicus Publications}, address = {G{\"o}ttingen}, issn = {1027-5606}, doi = {10.5194/hess-19-913-2015}, pages = {913 -- 931}, year = {2015}, abstract = {Climate change is likely to impact the seasonality and generation processes of floods in the Nordic countries, which has direct implications for flood risk assessment, design flood estimation, and hydropower production management. Using a multi-model/multi-parameter approach to simulate daily discharge for a reference (1961-1990) and a future (2071-2099) period, we analysed the projected changes in flood seasonality and generation processes in six catchments with mixed snowmelt/rainfall regimes under the current climate in Norway. The multi-model/multi-parameter ensemble consists of (i) eight combinations of global and regional climate models, (ii) two methods for adjusting the climate model output to the catchment scale, and (iii) one conceptual hydrological model with 25 calibrated parameter sets. Results indicate that autumn/winter events become more frequent in all catchments considered, which leads to an intensification of the current autumn/winter flood regime for the coastal catchments, a reduction of the dominance of spring/summer flood regimes in a high-mountain catchment, and a possible systematic shift in the current flood regimes from spring/summer to autumn/winter in the two catchments located in northern and south-eastern Norway. The changes in flood regimes result from increasing event magnitudes or frequencies, or a combination of both during autumn and winter. Changes towards more dominant autumn/winter events correspond to an increasing relevance of rainfall as a flood generating process (FGP) which is most pronounced in those catchments with the largest shifts in flood seasonality. Here, rainfall replaces snowmelt as the dominant FGP primarily due to increasing temperature.We further analysed the ensemble components in contributing to overall uncertainty in the projected changes and found that the climate projections and the methods for downscaling or bias correction tend to be the largest contributors. The relative role of hydrological parameter uncertainty, however, is highest for those catchments showing the largest changes in flood seasonality, which confirms the lack of robustness in hydrological model parameterization for simulations under transient hydrometeorological conditions.}, language = {en} } @misc{VormoorLawrenceHeistermannetal.2015, author = {Vormoor, Klaus Josef and Lawrence, D. and Heistermann, Maik and Bronstert, Axel}, title = {Climate change impacts on the seasonality and generation processes of floods}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-84366}, year = {2015}, abstract = {Climate change is likely to impact the seasonality and generation processes of floods in the Nordic countries, which has direct implications for flood risk assessment, design flood estimation, and hydropower production management. Using a multi-model/multi-parameter approach to simulate daily discharge for a reference (1961-1990) and a future (2071-2099) period, we analysed the projected changes in flood seasonality and generation processes in six catchments with mixed snowmelt/rainfall regimes under the current climate in Norway. The multi-model/multi-parameter ensemble consists of (i) eight combinations of global and regional climate models, (ii) two methods for adjusting the climate model output to the catchment scale, and (iii) one conceptual hydrological model with 25 calibrated parameter sets. Results indicate that autumn/winter events become more frequent in all catchments considered, which leads to an intensification of the current autumn/winter flood regime for the coastal catchments, a reduction of the dominance of spring/summer flood regimes in a high-mountain catchment, and a possible systematic shift in the current flood regimes from spring/summer to autumn/winter in the two catchments located in northern and south-eastern Norway. The changes in flood regimes result from increasing event magnitudes or frequencies, or a combination of both during autumn and winter. Changes towards more dominant autumn/winter events correspond to an increasing relevance of rainfall as a flood generating process (FGP) which is most pronounced in those catchments with the largest shifts in flood seasonality. Here, rainfall replaces snowmelt as the dominant FGP primarily due to increasing temperature.We further analysed the ensemble components in contributing to overall uncertainty in the projected changes and found that the climate projections and the methods for downscaling or bias correction tend to be the largest contributors. The relative role of hydrological parameter uncertainty, however, is highest for those catchments showing the largest changes in flood seasonality, which confirms the lack of robustness in hydrological model parameterization for simulations under transient hydrometeorological conditions.}, language = {en} } @phdthesis{Karo2015, author = {Karo, Nihad Majeed}, title = {Metamorphic evolution of the Northern Zagros Suture Zone (NZSZ)}, school = {Universit{\"a}t Potsdam}, pages = {127}, year = {2015}, language = {en} } @phdthesis{Trauth2015, author = {Trauth, Nico}, title = {Flow and reactive transport modeling at the stream-groundwater interface}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-82748}, school = {Universit{\"a}t Potsdam}, pages = {xv, 103}, year = {2015}, abstract = {Stream water and groundwater are important fresh water resources but their water quality is deteriorated by harmful solutes introduced by human activities. The interface between stream water and the subsurface water is an important zone for retention, transformation and attenuation of these solutes. Streambed structures enhance these processes by increased water and solute exchange across this interface, denoted as hyporheic exchange. This thesis investigates the influence of hydrological and morphological factors on hyporheic water and solute exchange as well as redox-reactions in fluvial streambed structures on the intermediate scale (10-30m). For this purpose, a three-dimensional numerical modeling approach for coupling stream water flow with porous media flow is used. Multiple steady state stream water flow scenarios over different generic pool-riffle morphologies and a natural in-stream gravel bar are simulated by a computational fluid dynamics code that provides the hydraulic head distribution at the streambed. These heads are subsequently used as the top boundary condition of a reactive transport groundwater model of the subsurface beneath the streambed. Ambient groundwater that naturally interacts with the stream water is considered in scenarios of different magnitudes of downwelling stream water (losing case) and upwelling groundwater (gaining case). Also, the neutral case, where stream stage and groundwater levels are balanced is considered. Transport of oxygen, nitrate and dissolved organic carbon and their reaction by aerobic respiration and denitrification are modeled. The results show that stream stage and discharge primarily induce hyporheic exchange flux and solute transport with implications for specific residence times and reactions at both the fully and partially submerged structures. Gaining and losing conditions significantly diminish the extent of the hyporheic zone, the water exchange flux, and shorten residence times for both the fully and partially submerged structures. With increasing magnitude of gaining or losing conditions, these metrics exponentially decrease. Stream water solutes are transported mainly advectively into the hyporheic zone and hence their influx corresponds directly to the infiltrating water flux. Aerobic respiration takes place in the shallow streambed sediments, coinciding to large parts with the extent of the hyporheic exchange flow. Denitrification occurs mainly as a "reactive fringe" surrounding the aerobic zone, where oxygen concentration is low and still a sufficient amount of stream water carbon source is available. The solute consumption rates and the efficiency of the aerobic and anaerobic reactions depend primarily on the available reactive areas and the residence times, which are both controlled by the interplay between hydraulic head distribution at the streambed and the gradients between stream stage and ambient groundwater. Highest solute consumption rates can be expected under neutral conditions, where highest solute flux, longest residence times and largest extent of the hyporheic exchange occur. The results of this thesis show that streambed structures on the intermediate scale have a significant potential to contribute to a net solute turnover that can support a healthy status of the aquatic ecosystem.}, language = {en} } @phdthesis{Mulyukova2015, author = {Mulyukova, Elvira}, title = {Stability of the large low shear velocity provinces}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-82228}, school = {Universit{\"a}t Potsdam}, pages = {139}, year = {2015}, abstract = {We study segregation of the subducted oceanic crust (OC) at the core mantle boundary and its ability to accumulate and form large thermochemical piles (such as the seismically observed Large Low Shear Velocity Provinces - LLSVPs). Our high-resolution numerical simulations suggest that the longevity of LLSVPs for up to three billion years, and possibly longer, can be ensured by a balance in the rate of segregation of high-density OC-material to the CMB, and the rate of its entrainment away from the CMB by mantle upwellings. For a range of parameters tested in this study, a large-scale compositional anomaly forms at the CMB, similar in shape and size to the LLSVPs. Neutrally buoyant thermochemical piles formed by mechanical stirring - where thermally induced negative density anomaly is balanced by the presence of a fraction of dense anomalous material - best resemble the geometry of LLSVPs. Such neutrally buoyant piles tend to emerge and survive for at least 3Gyr in simulations with quite different parameters. We conclude that for a plausible range of values of density anomaly of OC material in the lower mantle - it is likely that it segregates to the CMB, gets mechanically mixed with the ambient material, and forms neutrally buoyant large scale compositional anomalies similar in shape to the LLSVPs. We have developed an efficient FEM code with dynamically adaptive time and space resolution, and marker-in-cell methodology. This enabled us to model thermochemical mantle convection at realistically high convective vigor, strong thermally induced viscosity variations, and long term evolution of compositional fields.}, language = {en} } @phdthesis{Heistermann2015, author = {Heistermann, Maik}, title = {Advancing weather radar in hydrology}, school = {Universit{\"a}t Potsdam}, pages = {228}, year = {2015}, language = {en} } @phdthesis{Pingel2015, author = {Pingel, Heiko}, title = {Mountain-range uplift \& climate-system interactions in the Southern Central Andes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-82301}, school = {Universit{\"a}t Potsdam}, pages = {xii, 178}, year = {2015}, abstract = {Zwei h{\"a}ufig diskutierte Aspekte der sp{\"a}tk{\"a}nozoischen Gebirgsbildung der Anden sind der Zeitpunkt sowie die Art und Weise der Heraushebung des Puna-Plateaus und seiner Randgebiete innerhalb der Ostkordillere und die damit verbundenen klimatischen {\"A}nderungen in NW Argentinien. Die Ostkordillere trennt die Bereiche des endorheischen, ariden Plateaus von semiariden und extern entw{\"a}sserten intermontanen Becken sowie dem humiden Andenvorland im Osten. Diese Unterschiede verdeutlichen die Bedeutung der {\"o}stlichen Flanken der Anden als orografische Barrieren gegen{\"u}ber feuchten Luftmassen aus dem Osten und spiegelt sich auch in ausgepr{\"a}gten Relief- und Topografiegradienten, der Niederschlagsverteilung, und der Effizienz von Oberfl{\"a}chenprozessen wider. Obwohl das {\"u}bergeordnete Deformationsmuster in diesem Teil der Anden eine ostw{\"a}rts gerichtete Wanderung der Deformationsprozesse im Gebirge indiziert, gibt es hier keine klar definierte Deformationsfront. Hebungsvorg{\"a}nge und die damit im Zusammenhang stehenden Sedimentprozesse setzen r{\"a}umlich und zeitlich sehr unterschiedlich ein. Zudem gestalten periodisch wiederkehrende Deformationsereignisse innerhalb intermontaner Becken und diachrone Hebungsvorg{\"a}nge, durch Reaktivierung {\"a}lterer Sockelstrukturen im Vorland, eine detaillierte Auswertung der r{\"a}umlich-zeitlichen Hebungsmuster zus{\"a}tzlich schwierig. Die vorliegende Arbeit konzentriert sich haupts{\"a}chlich auf die tektonische Entwicklung der Ostkordillere im Nordwesten Argentiniens, die Ablagerungsgeschichte ihrer intermontanen Sedimentbecken und die topografische Entwicklung der Ostflanke des andinen Puna-Plateaus. Im Allgemeinen sind sich die Sedimentbecken der Ostkordillere und der angrenzenden Provinzen, den Sierras Pampeanas und der Santa B{\´a}rbara Region, den durch St{\"o}rungen begrenzten und mit Sedimenten verf{\"u}llten Becken der hochandinen Plateauregion sehr {\"a}hnlich. Deutliche Unterschiede zur Puna bestehen aber dennoch, denn wiederholte Deformations-, Erosions- und Sedimentationsprozesse haben in den intermontanen Becken zu einer vielf{\"a}ltigen Stratigrafie, {\"U}berlagerungsprozessen und einer durch tektonische Prozesse und klimatischen Wandel charakterisierten Landschaft beigetragen. Je nach Erhaltungsgrad k{\"o}nnen in einigen F{\"a}llen Spuren dieser sediment{\"a}ren und tektonischen Entwicklung bis in die Zeit zur{\"u}ckreichen, als diese Bereiche des Gebirges noch Teil eines zusammenh{\"a}ngenden und unverformten Vorlandbeckens waren. Im Nordwesten Argentiniens enthalten k{\"a}nozoische Sedimente zahlreiche datierbare und geochemisch korrelierbare Vulkanaschen, die nicht nur als wichtige Leithorizonte zur Entschl{\"u}sselung tektonischer und sediment{\"a}rer Ereignisse dienen. Die vulkanischen Gl{\"a}ser dieser Aschen archivieren außerdem Wasserstoff-Isotopenverh{\"a}ltnisse fr{\"u}herer Oberfl{\"a}chenwasser, mit deren Hilfe - im Vergleich mit den Isotopenverh{\"a}ltnissen rezenter meteorischer W{\"a}sser - die r{\"a}umliche und zeitliche Entstehung orografischer Barrieren und tektonisch erzwungene Klima- und Umweltver{\"a}nderungen verfolgt werden k{\"o}nnen. Uran-Blei-Datierungen an Zirkonen aus den vulkanischen Aschelagen und die Rekonstruktion sediment{\"a}rer Pal{\"a}otransportrichtungen im intermontanen Humahuaca-Becken in der Ostkordillere (23.5° S) deuten an, dass das heutige Becken bis vor etwa 4.2 Ma Bestandteil eines gr{\"o}ßtenteils uneingeschr{\"a}nkten Ablagerungsbereichs war, der sich bis ins Vorland erstreckt haben muss. Deformation und Hebung {\"o}stlich des heutigen Beckens sorgten dabei f{\"u}r eine fortschreitende Entkopplung des Entw{\"a}sserungsnetzes vom Vorland und eine Umlenkung der Flussl{\"a}ufe nach S{\"u}den. In der Folge erzwang die weitere Hebung der Gebirgsbl{\"o}cke das Abregnen {\"o}stlicher Luftmassen in immer {\"o}stlicher gelegene Bereiche. Zudem k{\"o}nnen periodische Schwankungen der hydrologischen Verbindung des Beckens mit dem Vorland im Zusammenhang mit der Ablagerung und Erosion m{\"a}chtiger Beckenf{\"u}llungen identifiziert werden. Systematische Beziehungen zwischen Verwerfungen, regionalen Diskontinuit{\"a}ten und verstellten Terrassenfl{\"a}chen verweisen außerdem auf ein generelles Muster beckeninterner Deformation, vermutlich als Folge umfangreicher Beckenerosion und damit verbundenen {\"A}nderungen im tektonischen Spannungsfeld der Region. Einige dieser Beobachtungen k{\"o}nnen anhand ver{\"a}nderter Wasserstoff-Isotopenkonzentrationen vulkanischer Gl{\"a}ser aus der k{\"a}nozoischen Stratigrafie untermauert werden. Die δDg-Werte zeigen zwei wesentliche Trends, die einerseits in Verbindung mit Oberfl{\"a}chenhebung innerhalb des Einzugsgebiets zwischen 6.0 und 3.5 Ma stehen und andererseits mit dem Einsetzen semiarider Bedingungen durch Erreichen eines Schwellenwertes der Topografie der {\"o}stlich gelegenen Gebirgsz{\"u}ge nach 3.5 Ma erkl{\"a}rt werden k{\"o}nnen. Tektonisch bedingte Unterbrechung der Sedimentzufuhr aus westlich gelegenen Liefergebieten um 4.2 Ma und die folgende Hinterland-Aridifizierung deuten weiterhin auf die M{\"o}glichkeit hin, dass diese Prozesse die Folge eines lateralen Wachstums des Puna-Plateaus sind. Diese Aridifizierung im Bereich der Puna resultierte in einem ineffizienten, endorheischen Entw{\"a}sserungssystem, das dazu beigetragen hat, das Plateau vor Einschneidung und externer Entw{\"a}sserung zu bewahren und Reliefgegens{\"a}tze aufgrund fortgesetzter Beckensedimentation reduzierte. Die diachrone Natur der Hebungen und Beckenbildungen sowie deren Auswirkungen auf das Flusssystem im angrenzenden Vorland wird sowohl durch detaillierte Analysen der Sedimentherkunft und Transportrichtungen als auch Uran-Blei-Datierungen im Lerma- und Met{\´a}n-Becken (25° S) weiterhin unterstrichen. Das wird besonders deutlich am Beispiel der isolierten Hebung der Sierra de Met{\´a}n vor etwa 10 Ma, die mehr als 50 km von der aktiven orogenen Front im Westen entfernt liegt. Ab 5 Ma sind typische Lithologien der Puna nicht mehr in den Vorlandsedimenten nachweisbar, welches die weitere Hebung innerhalb der Ostkordillere und die hydrologische Isolation des Angastaco-Beckens in dieser Region dokumentiert. Im Sp{\"a}tplioz{\"a}n und Quart{\"a}r ist die Deformation letztlich {\"u}ber das gesamte Vorland verteilt und bis heute aktiv. Um die Beziehungen zwischen tektonisch kontrollierten Ver{\"a}nderungen der Topografie und deren Einfluss auf atmosph{\"a}rische Prozesse besser zu verstehen, werden in dieser Arbeit weitere altersspezifische Wasserstoff-Isotopendaten vulkanischer Gl{\"a}ser aus dem zerbrochenen Vorland, dem Angastaco-Becken in der {\"U}bergangsregion zwischen Ostkordillere und Punarand und anderer intermontaner Becken weiter s{\"u}dlich vorgestellt. Die Resultate dokumentieren {\"a}hnliche H{\"o}henlagen der untersuchten Regionen bis ca. 7 Ma, gefolgt von Hebungsprozessen im Bereich des Angastaco-Beckens. Ein Vergleich mit Isotopendaten vom benachbarten Puna-Plateau hilft abrupte δDg-Schwankungen in den intermontanen Daten zu erkl{\"a}ren und untermauert die Existenz wiederkehrender Phasen verst{\"a}rkt konvektiver Wetterlagen im Plioz{\"a}n, {\"a}hnlich heutigen Bedingungen. In dieser Arbeit werden gel{\"a}ndeorientierte und geochemische Methoden kombiniert, um Erkenntnisse {\"u}ber die Abl{\"a}ufe von topografiebildenden Deformations- und Hebungsprozessen zu gewinnen und Wechselwirkungen mit der daraus resultierenden Niederschlagsverteilung, Erosion und Sedimentation innerhalb tektonisch aktiver Gebirge zu erforschen. Diese Erkenntnisse sind f{\"u}r ein besseres Verst{\"a}ndnis von Subduktionsgebirgen essentiell, besonders hinsichtlich des Deformationsstils und der zeitlich-r{\"a}umlichen Beziehungen bei der Hebung und Sedimentbeckenbildung. Diese Arbeit weist dar{\"u}berhinaus auf die Bedeutung stabiler Isotopensysteme zur Beantwortung pal{\"a}oaltimetrischer Fragestellungen und zur Erforschung von Pal{\"a}oumweltbedingungen hin und liefert wichtige Erkenntnisse f{\"u}r einen kritischen Umgang mit solchen Daten in anderen Regionen.}, language = {en} } @phdthesis{Tian2014, author = {Tian, Fang}, title = {Vegetation and environmental changes on millennial, centennial and decadal time-scales in central Mongolia and their driving forces}, school = {Universit{\"a}t Potsdam}, pages = {139}, year = {2014}, language = {en} } @phdthesis{Gassmoeller2014, author = {Gaßm{\"o}ller, Ren{\´e}}, title = {The interaction of subducted slabs and plume generation zones in geodynamic models}, school = {Universit{\"a}t Potsdam}, pages = {158}, year = {2014}, language = {en} } @phdthesis{Mueller2015, author = {M{\"u}ller, Eva Nora}, title = {The ecohydrological transfers, interactions and degradation arising from high-intensity storm events}, school = {Universit{\"a}t Potsdam}, pages = {224}, year = {2015}, language = {en} } @phdthesis{Rohrmann2015, author = {Rohrmann, Alexander}, title = {The role of wind and water in shaping earth's plateaus}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-77938}, school = {Universit{\"a}t Potsdam}, pages = {XXV, 157}, year = {2015}, abstract = {The overarching goal of this dissertation is to provide a better understanding of the role of wind and water in shaping Earth's Cenozoic orogenic plateaus - prominent high-elevation, low relief sectors in the interior of Cenozoic mountain belts. In particular, the feedbacks between surface uplift, the build-up of topography and ensuing changes in precipitation, erosion, and vegetation patterns are addressed in light of past and future climate change. Regionally, the study focuses on the two world's largest plateaus, the Altiplano-Puna Plateau of the Andes and Tibetan Plateau, both characterized by average elevations of >4 km. Both plateaus feature high, deeply incised flanks with pronounced gradients in rainfall, vegetation, hydrology, and surface processes. These characteristics are rooted in the role of plateaus to act as efficient orographic barriers to rainfall and to force changes in atmospheric flow. The thesis examines the complex topics of tectonic and climatic forcing of the surface-process regime on three different spatial and temporal scales: (1) bedrock wind-erosion rates are quantified in the arid Qaidam Basin of NW Tibet over millennial timescales using cosmogenic radionuclide dating; (2) present-day stable isotope composition in rainfall is examined across the south-central Andes in three transects between 22° S and 28° S; these data are modeled and assessed with remotely sensed rainfall data of the Tropical Rainfall Measuring Mission and the Moderate Resolution Imaging Spectroradiometer; (3) finally, a 2.5-km-long Mio-Pliocene sedimentary record of the intermontane Angastaco Basin (25°45' S, 66°00' W) is presented in the context of hydrogen and carbon compositions of molecular lipid biomarker, and oxygen and carbon isotopes obtained from pedogenic carbonates; these records are compared to other environmental proxies, including hydrated volcanic glass shards from volcanic ashes intercalated in the sedimentary strata. There are few quantitative estimates of eolian bedrock-removal rates from arid, low relief landscapes. Wind-erosion rates from the western Qaidam Basin based on cosmogenic 10Be measurements document erosion rates between 0.05 to 0.4 mm/yr. This finding indicates that in arid environments with strong winds, hyperaridity, exposure of friable strata, and ongoing rock deformation and uplift, wind erosion can outpace fluvial erosion. Large eroded sediment volumes within the Qaidam Basin and coeval dust deposition on the Chinese Loess plateau, exemplify the importance of dust production within arid plateau environments for marine and terrestrial depositional processes, but also health issues and fertilization of soils. In the south-central Andes, the analysis of 234 stream-water samples for oxygen and hydrogen reveals that areas experiencing deep convective storms do not show the commonly observed patterns of isotopic fractionation and the expected co-varying relationships between oxygen and hydrogen with increasing elevation. These convective storms are formed over semi-arid intermontane basins in the transition between the broken foreland of the Sierras Pampeanas, the Eastern Cordillera, and the Puna Plateau in the interior of the orogen. Here, convective rainfall dominates the precipitation budget and no systematic stable isotope-elevation relationship exists. Regions to the north, in the transition between the broken foreland and the Subandean foreland fold-and-thrust belt, the impact of convection is subdued, with lower degrees of storminess and a stronger expected isotope-elevation relationship. This finding of present-day fractionation trends of meteoric water is of great importance for paleoenvironmental studies in attempts to use stable isotope relationships in the reconstruction of paleoelevations. The third part of the thesis focuses on the paleohydrological characteristics of the Mio-Pliocene (10-2 Ma) Angastaco Basin sedimentary record, which reveals far-reaching environmental changes during Andean uplift and orographic barrier formation. A precipitation- evapotranspiration record identifies the onset of a precipitation regime related to the South American Low Level Jet at this latitude after 9 Ma. Humid foreland conditions existed until 7 Ma, followed by orographic barrier uplift to the east of the present-day Angastaco Basin. This was superseded by rapid (~0.5 Myr) aridification in an intermontane basin, highlighting the effects of eastward-directed deformation. A transition in vegetation cover from a humid C3 forest ecosystem to semi-arid C4-dominated vegetation was coeval with continued basin uplift to modern elevations.}, language = {en} } @phdthesis{Pussak2014, author = {Pussak, Marcin}, title = {Seismic characterization of geothermal reservoirs by application of the common-reflection-surface stack method and attribute analysis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-77565}, school = {Universit{\"a}t Potsdam}, pages = {viii, 140}, year = {2014}, abstract = {An important contribution of geosciences to the renewable energy production portfolio is the exploration and utilization of geothermal resources. For the development of a geothermal project at great depths a detailed geological and geophysical exploration program is required in the first phase. With the help of active seismic methods high-resolution images of the geothermal reservoir can be delivered. This allows potential transport routes for fluids to be identified as well as regions with high potential of heat extraction to be mapped, which indicates favorable conditions for geothermal exploitation. The presented work investigates the extent to which an improved characterization of geothermal reservoirs can be achieved with the new methods of seismic data processing. The summations of traces (stacking) is a crucial step in the processing of seismic reflection data. The common-reflection-surface (CRS) stacking method can be applied as an alternative for the conventional normal moveout (NMO) or the dip moveout (DMO) stack. The advantages of the CRS stack beside an automatic determination of stacking operator parameters include an adequate imaging of arbitrarily curved geological boundaries, and a significant increase in signal-to-noise (S/N) ratio by stacking far more traces than used in a conventional stack. A major innovation I have shown in this work is that the quality of signal attributes that characterize the seismic images can be significantly improved by this modified type of stacking in particular. Imporoved attribute analysis facilitates the interpretation of seismic images and plays a significant role in the characterization of reservoirs. Variations of lithological and petro-physical properties are reflected by fluctuations of specific signal attributes (eg. frequency or amplitude characteristics). Its further interpretation can provide quality assessment of the geothermal reservoir with respect to the capacity of fluids within a hydrological system that can be extracted and utilized. The proposed methodological approach is demonstrated on the basis on two case studies. In the first example, I analyzed a series of 2D seismic profile sections through the Alberta sedimentary basin on the eastern edge of the Canadian Rocky Mountains. In the second application, a 3D seismic volume is characterized in the surroundings of a geothermal borehole, located in the central part of the Polish basin. Both sites were investigated with the modified and improved stacking attribute analyses. The results provide recommendations for the planning of future geothermal plants in both study areas.}, language = {en} } @phdthesis{Reiter2014, author = {Reiter, Karsten}, title = {Crustal stress variability across spatial scales - examples from Canada, Northern Switzerland and a South African gold mine}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-76762}, school = {Universit{\"a}t Potsdam}, pages = {VIII, 149, XI}, year = {2014}, abstract = {The quantitative descriptions of the state of stress in the Earth's crust, and spatial-temporal stress changes are of great importance in terms of scientific questions as well as applied geotechnical issues. Human activities in the underground (boreholes, tunnels, caverns, reservoir management, etc.) have a large impact on the stress state. It is important to assess, whether these activities may lead to (unpredictable) hazards, such as induced seismicity. Equally important is the understanding of the in situ stress state in the Earth's crust, as it allows the determination of safe well paths, already during well planning. The same goes for the optimal configuration of the injection- and production wells, where stimulation for artificial fluid path ways is necessary. The here presented cumulative dissertation consists of four separate manuscripts, which are already published, submitted or will be submitted for peer review within the next weeks. The main focus is on the investigation of the possible usage of geothermal energy in the province Alberta (Canada). A 3-D geomechanical-numerical model was designed to quantify the contemporary 3-D stress tensor in the upper crust. For the calibration of the regional model, 321 stress orientation data and 2714 stress magnitude data were collected, whereby the size and diversity of the database is unique. A calibration scheme was developed, where the model is calibrated versus the in situ stress data stepwise for each data type and gradually optimized using statistically test methods. The optimum displacement on the model boundaries can be determined by bivariate linear regression, based on only three model runs with varying deformation ratio. The best-fit model is able to predict most of the in situ stress data quite well. Thus, the model can provide the full stress tensor along any chosen virtual well paths. This can be used to optimize the orientation of horizontal wells, which e.g. can be used for reservoir stimulation. The model confirms regional deviations from the average stress orientation trend, such as in the region of the Peace River Arch and the Bow Island Arch. In the context of data compilation for the Alberta stress model, the Canadian database of the World Stress Map (WSM) could be expanded by including 514 new data records. This publication of an update of the Canadian stress map after ~20 years with a specific focus on Alberta shows, that the maximum horizontal stress (SHmax) is oriented southwest to northeast over large areas in Northern America. The SHmax orientation in Alberta is very homogeneous, with an average of about 47°. In order to calculate the average SHmax orientation on a regular grid as well as to estimate the wave-length of stress orientation, an existing algorithm has been improved and is applied to the Canadian data. The newly introduced quasi interquartile range on the circle (QIROC) improves the variance estimation of periodic data, as it is less susceptible to its outliers. Another geomechanical-numerical model was built to estimate the 3D stress tensor in the target area "N{\"o}rdlich L{\"a}gern" in Northern Switzerland. This location, with Opalinus clay as a host rock, is a potential repository site for high-level radioactive waste. The performed modelling aims to investigate the sensitivity of the stress tensor on tectonic shortening, topography, faults and variable rock properties within the Mesozoic sedimentary stack, according to the required stability needed for a suitable radioactive waste disposal site. The majority of the tectonic stresses caused by the far-field shortening from the South are admitted by the competent rock units in the footwall and hanging wall of the argillaceous target horizon, the Upper Malm and Upper Muschelkalk. Thus, the differential stress within the host rock remains relatively low. East-west striking faults release stresses driven by tectonic shortening. The purely gravitational influence by the topography is low; higher SHmax magnitudes below topographical depression and lower values below hills are mainly observed near the surface. A complete calibration of the model is not possible, as no stress magnitude data are available for calibration, yet. The collection of this data will begin in 2015; subsequently they will be used to adjust the geomechanical-numerical model again. The third geomechanical-numerical model investigates the stress variation in an ultra-deep gold mine in South Africa. This reservoir model is spatially one order of magnitude smaller than the previous local model from Northern Switzerland. Here, the primary focus is to investigate the hypothesis that the Mw 1.9 earthquake on 27 December 2007 was induced by stress changes due to the mining process. The Coulomb failure stress change (DeltaCFS) was used to analyse the stress change. It confirmed that the seismic event was induced by static stress transfer due to the mining progress. The rock was brought closer to failure on the derived rupture plane by stress changes of up to 1.5-15MPa, in dependence of the DeltaCFS analysis type. A forward modelling of a generic excavation scheme reveals that with decreasing distance to the dyke the DeltaCFS values increase significantly. Hence, even small changes in the mining progress can have a significant impact on the seismic hazard risk, i.e. the change of the occurrence probability to induce a seismic event of economic concern.}, language = {en} } @phdthesis{Busch2015, author = {Busch, Jan Philip}, title = {Investigations on mobility of carbon colloid supported nanoscale zero-valent iron (nZVI) for groundwater remediation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-76873}, school = {Universit{\"a}t Potsdam}, pages = {X, 127, XLIII}, year = {2015}, abstract = {Injection of nanoscale zero-valent iron (nZVI) is an innovative technology for in situ installation of a permeable reactive barrier in the subsurface. Zerovalent iron (ZVI) is highly reactive with chlorinated hydrocarbons (CHCs) and renders them into less harmful substances. Application of nZVI instead of granular ZVI can increase rates of dechlorination of CHCs by orders of magnitude, due to its higher surface area. This approach is still difficult to apply due to fast agglomeration and sedimentation of colloidal suspensions of nZVI, which leads to very short transport distances. To overcome this issue of limited mobility, polyanionic stabilisers are added to increase surface charge and stability of suspensions. In field experiments maximum transport distances of a few metres were achieved. A new approach, which is investigated in this thesis, is enhanced mobility of nZVI by a more mobile carrier colloid. The investigated composite material consists of activated carbon, which is loaded with nZVI. In this cumulative thesis, transport characteristics of carbon-colloid supported nZVI (c-nZVI) are investigated. Investigations started with column experiments in 40 cm columns filled with various porous media to investigate on physicochemical influences on transport characteristics. The experimental setup was enlarged to a transport experiment in a 1.2-m-sized two-dimensional aquifer tank experiment, which was filled with granular porous media. Further, a field experiment was performed in a natural aquifer system with a targeted transport distance of 5.3 m. Parallel to these investigations, alternative methods for transport observations were investigated by using noninvasive tomographic methods. Experiments using synchrotron radiation and magnetic resonance (MRI) were performed to investigate in situ transport characteristics in a non-destructive way. Results from column experiments show potentially high mobility under environmental relevant conditions. Addition of mono-and bivalent salts, e.g. more than 0.5 mM/L CaCl2, might decrease mobility. Changes in pH to values below 6 can inhibit mobility at all. Measurements of colloid size show changes in the mean particle size by a factor of ten. Measurements of zeta potential revealed an increase of -62 mV to -82 mV. Results from the 2D-aquifer test system suggest strong particle deposition in the first centimetres and only weak straining in the further travel path and no gravitational influence on particle transport. Straining at the beginning of the travel path in the porous medium was observed with tomographic investigations of transport. MRI experiments revealed similar results to the previous experiments, and observations using synchrotron radiation suggest straining of colloids at pore throats. The potential for high transport distances, which was suggested from laboratory experiments, was confirmed in the field experiment, where the transport distance of 5.3 m was reached by at least 10\% of injected nZVI. Altogether, transport distances of the investigated carbon-colloid supported nZVI are higher than published results of traditional nZVI.}, language = {en} } @phdthesis{Sen2014, author = {Sen, Ali Tolga}, title = {Inversion of seismic source parameters for weak mining-induced and natural earthquakes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71914}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {The purpose of this thesis is to develop an automated inversion scheme to derive point and finite source parameters for weak earthquakes, here intended with the unusual meaning of earthquakes with magnitudes at the limit or below the bottom magnitude threshold of standard source inversion routines. The adopted inversion approaches entirely rely on existing inversion software, the methodological work mostly targeting the development and tuning of optimized inversion flows. The resulting inversion scheme is tested for very different datasets, and thus allows the discussion on the source inversion problem at different scales. In the first application, dealing with mining induced seismicity, the source parameters determination is addressed at a local scale, with source-sensor distance of less than 3 km. In this context, weak seismicity corresponds to event below magnitude MW 2.0, which are rarely target of automated source inversion routines. The second application considers a regional dataset, namely the aftershock sequence of the 2010 Maule earthquake (Chile), using broadband stations at regional distances, below 300 km. In this case, the magnitude range of the target aftershocks range down to MW 4.0. This dataset is here considered as a weak seismicity case, since the analysis of such moderate seismicity is generally investigated only by moment tensor inversion routines, with no attempt to resolve source duration or finite source parameters. In this work, automated multi-step inversion schemes are applied to both datasets with the aim of resolving point source parameters, both using double couple (DC) and full moment tensor (MT) models, source duration and finite source parameters. A major result of the analysis of weaker events is the increased size of resulting moment tensor catalogues, which interpretation may become not trivial. For this reason, a novel focal mechanism clustering approach is used to automatically classify focal mechanisms, allowing the investigation of the most relevant and repetitive rupture features. The inversion of the mining induced seismicity dataset reveals the repetitive occurrence of similar rupture processes, where the source geometry is controlled by the shape of the mined panel. Moreover, moment tensor solutions indicate a significant contribution of tensile processes. Also the second application highlights some characteristic geometrical features of the fault planes, which show a general consistency with the orientation of the slab. The additional inversion for source duration allowed to verify the empirical correlation for moment normalized earthquakes in subduction zones among a decreasing rupture duration with increasing source depth, which was so far only observed for larger events.}, language = {en} } @phdthesis{Cao2014, author = {Cao, Xianyong}, title = {Vegetation and climate change in eastern continental Asia during the last 22 ka inferred from pollen data synthesis}, pages = {156}, year = {2014}, language = {en} } @phdthesis{Sarkar2014, author = {Sarkar, Saswati}, title = {Holocene variations in the strength of the Indian Monsoon system}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74905}, school = {Universit{\"a}t Potsdam}, pages = {ix, 114}, year = {2014}, abstract = {The monsoon is an important component of the Earth's climate system. It played a vital role in the development and sustenance of the largely agro-based economy in India. A better understanding of past variations in the Indian Summer Monsoon (ISM) is necessary to assess its nature under global warming scenarios. Instead, our knowledge of spatiotemporal patterns of past ISM strength, as inferred from proxy records, is limited due to the lack of high-resolution paleo-hydrological records from the core monsoon domain. In this thesis I aim to improve our understanding of Holocene ISM variability from the core 'monsoon zone' (CMZ) in India. To achieve this goal, I tried to understand modern and thereafter reconstruct Holocene monsoonal hydrology, by studying surface sediments and a high-resolution sedimentary record from the saline-alkaline Lonar crater lake, central India. My approach relies on analyzing stable carbon and hydrogen isotope ratios from sedimentary lipid biomarkers to track past hydrological changes. In order to evaluate the relationship of the modern ecosystem and hydrology of the lake I studied the distribution of lipid biomarkers in the modern ecosystem and compared it to lake surface sediments. The major plants from dry deciduous mixed forest type produced a greater amount of leaf wax n-alkanes and a greater fraction of n-C31 and n-C33 alkanes relative to n-C27 and n-C29. Relatively high average chain length (ACL) values (29.6-32.8) for these plants seem common for vegetation from an arid and warm climate. Additionally I found that human influence and subsequent nutrient supply result in increased lake primary productivity, leading to an unusually high concentration of tetrahymanol, a biomarker for salinity and water column stratification, in the nearshore sediments. Due to this inhomogeneous deposition of tetrahymanol in modern sediments, I hypothesize that lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments, in addition to source changes. I reconstructed centennial-scale hydrological variability associated with changes in the intensity of the ISM based on a record of leaf wax and aquatic biomarkers and their stable carbon (δ13C) and hydrogen (δD) isotopic composition from a 10 m long sediment core from the lake. I identified three main periods of distinct hydrology over the Holocene in central India. The period between 10.1 and 6 cal. ka BP was likely the wettest during the Holocene. Lower ACL index values (29.4 to 28.6) of leaf wax n-alkanes and their negative δ13C values (-34.8 per mille to -27.8 per mille) indicated the dominance of woody C3 vegetation in the catchment, and negative δDwax (average for leaf wax n-alkanes) values (-171 per mille to -147 per mille) argue for a wet period due to an intensified monsoon. After 6 cal. ka BP, a gradual shift to less negative δ13C values (particularly for the grass derived n-C31) and appearance of the triterpene lipid tetrahymanol, generally considered as a marker for salinity and water column stratification, marked the onset of drier conditions. At 5.1 cal. ka BP increasing flux of leaf wax n-alkanes along with the highest flux of tetrahymanol indicated proximity of the lakeshore to the center due to a major lake level decrease. Rapid fluctuations in abundance of both terrestrial and aquatic biomarkers between 4.8 and 4 cal. ka BP indicated an unstable lake ecosystem, culminating in a transition to arid conditions. A pronounced shift to less negative δ13C values, in particular for n-C31 (-25.2 per mille to -22.8 per mille), over this period indicated a change of dominant vegetation to C4 grasses. Along with a 40 per mille increase in leaf wax n-alkane δD values, which likely resulted from less rainfall and/or higher plant evapotranspiration, I interpret this period to reflect the driest conditions in the region during the last 10.1 ka. This transition led to protracted late Holocene arid conditions and the establishment of a permanently saline lake. This is supported by the high abundance of tetrahymanol. A late Holocene peak of cyanobacterial biomarker input at 1.3 cal. ka BP might represent an event of lake eutrophication, possibly due to human impact and the onset of cattle/livestock farming in the catchment. The most intriguing feature of the mid-Holocene driest period was the high amplitude and rapid fluctuations in δDwax values, probably due to a change in the moisture source and/or precipitation seasonality. I hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation were responsible for an unstable hydroclimate in the mid-Holocene in the CMZ. My findings shed light onto the sequence of changes during mean state changes of the monsoonal system, once an insolation driven threshold has been passed, and show that small changes in solar insolation can be associated to major environmental changes and large fluctuations in moisture source, a scenario that may be relevant with respect to future changes in the ISM system.}, language = {en} } @phdthesis{Borchardt2014, author = {Borchardt, Sven}, title = {Rainfall, weathering and erosion}, pages = {x, 90}, year = {2014}, language = {en} } @phdthesis{Feld2014, author = {Feld, Christian}, title = {Crustal structure of the Eratosthenes Seamount, Cyprus and S. Turkey from an amphibian wide-angle seismic profile}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-73479}, school = {Universit{\"a}t Potsdam}, pages = {xi, 131}, year = {2014}, abstract = {In March 2010, the project CoCoCo (incipient COntinent-COntinent COllision) recorded a 650 km long amphibian N-S wide-angle seismic profile, extending from the Eratosthenes Seamount (ESM) across Cyprus and southern Turkey to the Anatolian plateau. The aim of the project is to reveal the impact of the transition from subduction to continent-continent collision of the African plate with the Cyprus-Anatolian plate. A visual quality check, frequency analysis and filtering were applied to the seismic data and reveal a good data quality. Subsequent first break picking, finite-differences ray tracing and inversion of the offshore wide-angle data leads to a first-arrival tomographic model. This model reveals (1) P-wave velocities lower than 6.5 km/s in the crust, (2) a variable crustal thickness of about 28 - 37 km and (3) an upper crustal reflection at 5 km depth beneath the ESM. Two land shots on Turkey, also recorded on Cyprus, airgun shots south of Cyprus and geological and previous seismic investigations provide the information to derive a layered velocity model beneath the Anatolian plateau and for the ophiolite complex on Cyprus. The analysis of the reflections provides evidence for a north-dipping plate subducting beneath Cyprus. The main features of this layered velocity model are (1) an upper and lower crust with large lateral changes of the velocity structure and thickness, (2) a Moho depth of about 38 - 45 km beneath the Anatolian plateau, (3) a shallow north-dipping subducting plate below Cyprus with an increasing dip and (4) a typical ophiolite sequence on Cyprus with a total thickness of about 12 km. The offshore-onshore seismic data complete and improve the information about the velocity structure beneath Cyprus and the deeper part of the offshore tomographic model. Thus, the wide-angle seismic data provide detailed insights into the 2-D geometry and velocity structures of the uplifted and overriding Cyprus-Anatolian plate. Subsequent gravity modelling confirms and extends the crustal P-wave velocity model. The deeper part of the subducting plate is constrained by the gravity data and has a dip angle of ~ 28°. Finally, an integrated analysis of the geophysical and geological information allows a comprehensive interpretation of the crustal structure related to the collision process.}, language = {en} } @phdthesis{Tympel2014, author = {Tympel, Jens G{\"u}nter}, title = {Numerical modeling of the Cenozoic Pamir-Tien Shan orogeny}, pages = {168}, year = {2014}, language = {en} } @phdthesis{Munack2014, author = {Munack, Henry}, title = {From phantom blocks to denudational noise}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-72629}, school = {Universit{\"a}t Potsdam}, pages = {xvii, 172}, year = {2014}, abstract = {Knowing the rates and mechanisms of geomorphic process that shape the Earth's surface is crucial to understand landscape evolution. Modern methods for estimating denudation rates enable us to quantitatively express and compare processes of landscape downwearing that can be traced through time and space—from the seemingly intact, though intensely shattered, phantom blocks of the catastrophically fragmented basal facies of giant rockslides up to denudational noise in orogen-wide data sets averaging over several millennia. This great variety of spatiotemporal scales of denudation rates is both boon and bane of geomorphic process rates. Indeed, processes of landscape downwearing can be traced far back in time, helping us to understand the Earth's evolution. Yet, this benefit may turn into a drawback due to scaling issues if these rates are to be compared across different observation timescales. This thesis investigates the mechanisms, patterns and rates of landscape downwearing across the Himalaya-Tibet orogen. Accounting for the spatiotemporal variability of denudation processes, this thesis addresses landscape downwearing on three distinctly different spatial scales, starting off at the local scale of individual hillslopes where considerable amounts of debris are generated from rock instantaneously: Rocksliding in active mountains is a major impetus of landscape downwearing. Study I provides a systematic overview of the internal sedimentology of giant rockslide deposits and thus meets the challenge of distinguishing them from macroscopically and microscopically similar glacial deposits, tectonic fault-zone breccias, and impact breccias. This distinction is important to avoid erroneous or misleading deduction of paleoclimatic or tectonic implications. -> Grain size analysis shows that rockslide-derived micro-breccia closely resemble those from meteorite impact or tectonic faults. -> Frictionite may occur more frequently that previously assumed. -> M{\"o}ssbauer-spectroscopy derived results indicate basal rock melting in the absence of water, involving short-term temperatures of >1500°C. Zooming out, Study II tracks the fate of these sediments, using the example of the upper Indus River, NW India. There we use river sand samples from the Indus and its tributaries to estimate basin-averaged denudation rates along a ~320-km reach across the Tibetan Plateau margin, to answer the question whether incision into the western Tibetan Plateau margin is currently active or not. -> We find an about one-order-of-magnitude upstream decay—from 110 to 10 mm kyr^-1—of cosmogenic Be-10-derived basin-wide denudation rates across the morphological knickpoint that marks the transition from the Transhimalayan ranges to the Tibetan Plateau. This trend is corroborated by independent bulk petrographic and heavy mineral analysis of the same samples. -> From the observation that tributary-derived basin-wide denudation rates do not increase markedly until ~150-200 km downstream of the topographic plateau margin we conclude that incision into the Tibetan Plateau is inactive. -> Comparing our postglacial Be-10-derived denudation rates to long-term (>10^6 yr) estimates from low-temperature thermochronometry, ranging from 100 to 750 mm kyr^-1, points to an order- of-magnitude decay of rates of landscape downwearing towards present. We infer that denudation rates must have been higher in the Quaternary, probably promoted by the interplay of glacial and interglacial stages. Our investigation of regional denudation patterns in the upper Indus finally is an integral part of Study III that synthesizes denudation of the Himalaya-Tibet orogen. In order to identify general and time-invariant predictors for Be-10-derived denudation rates we analyze tectonic, climatic and topographic metrics from an inventory of 297 drainage basins from various parts of the orogen. Aiming to get insight to the full response distributions of denudation rate to tectonic, climatic and topographic candidate predictors, we apply quantile regression instead of ordinary least squares regression, which has been standard analysis tool in previous studies that looked for denudation rate predictors. -> We use principal component analysis to reduce our set of 26 candidate predictors, ending up with just three out of these: Aridity Index, topographic steepness index, and precipitation of the coldest quarter of the year. -> Topographic steepness index proves to perform best during additive quantile regression. Our consequent prediction of denudation rates on the basin scale involves prediction errors that remain between 5 and 10 mm kyr^-1. -> We conclude that while topographic metrics such as river-channel steepness and slope gradient—being representative on timescales that our cosmogenic Be-10-derived denudation rates integrate over—generally appear to be more suited as predictors than climatic and tectonic metrics based on decadal records.}, language = {en} } @phdthesis{Sayago2014, author = {Sayago, Jhosnella}, title = {Late Paleozoic basin analysis of the Loppa High and Finnmark Platform in the Norwegian Barents Sea : integration of seismic attributes and seismic sequence stratigraphy}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72576}, school = {Universit{\"a}t Potsdam}, pages = {viii, 109}, year = {2014}, abstract = {The subsurface upper Palaeozoic sedimentary successions of the Loppa High half-graben and the Finnmark platform in the Norwegian Barents Sea (southwest Barents Sea) were investigated using 2D/3D seismic datasets combined with well and core data. These sedimentary successions represent a case of mixed siliciclastic-carbonates depositional systems, which formed during the earliest phase of the Atlantic rifting between Greenland and Norway. During the Carboniferous and Permian the southwest part of the Barents Sea was located along the northern margin of Pangaea, which experienced a northward drift at a speed of ~2-3 mm per year. This gradual shift in the paleolatitudinal position is reflected by changes in regional climatic conditions: from warm-humid in the early Carboniferous, changing to warm-arid in the middle to late Carboniferous and finally to colder conditions in the late Permian. Such changes in paleolatitude and climate have resulted in major changes in the style of sedimentation including variations in the type of carbonate factories. The upper Palaeozoic sedimentary succession is composed of four major depositional units comprising chronologically the Billefjorden Group dominated by siliciclastic deposition in extensional tectonic-controlled wedges, the Gipsdalen Group dominated by warm-water carbonates, stacked buildups and evaporites, the Bjarmeland Group characterized by cool-water carbonates as well as by the presence of buildup networks, and the Tempelfjorden Group characterized by fine-grained sedimentation dominated by biological silica production. In the Loppa High, the integration of a core study with multi-attribute seismic facies classification allowed highlighting the main sedimentary unconformities and mapping the spatial extent of a buried paleokarst terrain. This geological feature is interpreted to have formed during a protracted episode of subaerial exposure occurring between the late Palaeozoic and middle Triassic. Based on seismic sequence stratigraphy analysis the palaeogeography in time and space of the Loppa High basin was furthermore reconstructed and a new and more detailed tectono-sedimentary model for this area was proposed. In the Finnmark platform area, a detailed core analysis of two main exploration wells combined with key 2D seismic sections located along the main depositional profile, allowed the evaluation of depositional scenarios for the two main lithostratigraphic units: the {\O}rn Formation (Gipsdalen Group) and the Isbj{\o}rn Formation (Bjarmeland Group). During the mid-Sakmarian, two major changes were observed between the two formations including (1) the variation in the type of the carbonate factories, which is interpreted to be depth-controlled and (2) the change in platform morphology, which evolved from a distally steepened ramp to a homoclinal ramp. The results of this study may help supporting future reservoirs characterization of the upper Palaeozoic units in the Barents Sea, particularly in the Loppa High half-graben and the Finmmark platform area.}, language = {en} } @phdthesis{Schollaen2014, author = {Schollaen, Karina}, title = {Tracking climate signals in tropical trees}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71947}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {The tropical warm pool waters surrounding Indonesia are one of the equatorial heat and moisture sources that are considered as a driving force of the global climate system. The climate in Indonesia is dominated by the equatorial monsoon system, and has been linked to El Ni{\~n}o-Southern Oscillation (ENSO) events, which often result in severe droughts or floods over Indonesia with profound societal and economic impacts on the populations living in the world's fourth most populated country. The latest IPCC report states that ENSO will remain the dominant mode in the tropical Pacific with global effects in the 21st century and ENSO-related precipitation extremes will intensify. However, no common agreement exists among climate simulation models for projected change in ENSO and the Australian-Indonesian Monsoon. Exploring high-resolution palaeoclimate archives, like tree rings or varved lake sediments, provide insights into the natural climate variability of the past, and thus helps improving and validating simulations of future climate changes. Centennial tree-ring stable isotope records | Within this doctoral thesis the main goal was to explore the potential of tropical tree rings to record climate signals and to use them as palaeoclimate proxies. In detail, stable carbon (δ13C) and oxygen (δ18O) isotopes were extracted from teak trees in order to establish the first well-replicated centennial (AD 1900-2007) stable isotope records for Java, Indonesia. Furthermore, different climatic variables were tested whether they show significant correlation with tree-ring proxies (ring-width, δ13C, δ18O). Moreover, highly resolved intra-annual oxygen isotope data were established to assess the transfer of the seasonal precipitation signal into the tree rings. Finally, the established oxygen isotope record was used to reveal possible correlations with ENSO events. Methodological achievements | A second goal of this thesis was to assess the applicability of novel techniques which facilitate and optimize high-resolution and high-throughput stable isotope analysis of tree rings. Two different UV-laser-based microscopic dissection systems were evaluated as a novel sampling tool for high-resolution stable isotope analysis. Furthermore, an improved procedure of tree-ring dissection from thin cellulose laths for stable isotope analysis was designed. The most important findings of this thesis are: I) The herein presented novel sampling techniques improve stable isotope analyses for tree-ring studies in terms of precision, efficiency and quality. The UV-laser-based microdissection serve as a valuable tool for sampling plant tissue at ultrahigh-resolution and for unprecedented precision. II) A guideline for a modified method of cellulose extraction from wholewood cross-sections and subsequent tree-ring dissection was established. The novel technique optimizes the stable isotope analysis process in two ways: faster and high-throughput cellulose extraction and precise tree-ring separation at annual to high-resolution scale. III) The centennial tree-ring stable isotope records reveal significant correlation with regional precipitation. High-resolution stable oxygen values, furthermore, allow distinguishing between dry and rainy season rainfall. IV) The δ18O record reveals significant correlation with different ENSO flavors and demonstrates the importance of considering ENSO flavors when interpreting palaeoclimatic data in the tropics. The findings of my dissertation show that seasonally resolved δ18O records from Indonesian teak trees are a valuable proxy for multi-centennial reconstructions of regional precipitation variability (monsoon signals) and large-scale ocean-atmosphere phenomena (ENSO) for the Indo-Pacific region. Furthermore, the novel methodological achievements offer many unexplored avenues for multidisciplinary research in high-resolution palaeoclimatology.}, language = {en} } @phdthesis{Radeff2014, author = {Radeff, Giuditta}, title = {Geohistory of the Central Anatolian Plateau southern margin (southern Turkey)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71865}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {The Adana Basin of southern Turkey, situated at the SE margin of the Central Anatolian Plateau is ideally located to record Neogene topographic and tectonic changes in the easternmost Mediterranean realm. Using industry seismic reflection data we correlate 34 seismic profiles with corresponding exposed units in the Adana Basin. The time-depth conversion of the interpreted seismic profiles allows us to reconstruct the subsidence curve of the Adana Basin and to outline the occurrence of a major increase in both subsidence and sedimentation rates at 5.45 - 5.33 Ma, leading to the deposition of almost 1500 km3 of conglomerates and marls. Our provenance analysis of the conglomerates reveals that most of the sediment is derived from and north of the SE margin of the Central Anatolian Plateau. A comparison of these results with the composition of recent conglomerates and the present drainage basins indicates major changes between late Messinian and present-day source areas. We suggest that these changes in source areas result of uplift and ensuing erosion of the SE margin of the plateau. This hypothesis is supported by the comparison of the Adana Basin subsidence curve with the subsidence curve of the Mut Basin, a mainly Neogene basin located on top of the Central Anatolian Plateau southern margin, showing that the Adana Basin subsidence event is coeval with an uplift episode of the plateau southern margin. The collection of several fault measurements in the Adana region show different deformation styles for the NW and SE margins of the Adana Basin. The weakly seismic NW portion of the basin is characterized by extensional and transtensional structures cutting Neogene deposits, likely accomodating the differential uplift occurring between the basin and the SE margin of the plateau. We interpret the tectonic evolution of the southern flank of the Central Anatolian Plateau and the coeval subsidence and sedimentation in the Adana Basin to be related to deep lithospheric processes, particularly lithospheric delamination and slab break-off.}, language = {en} } @phdthesis{Bach2013, author = {Bach, Christoph}, title = {Improving statistical seismicity models}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70591}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Several mechanisms are proposed to be part of the earthquake triggering process, including static stress interactions and dynamic stress transfer. Significant differences of these mechanisms are particularly expected in the spatial distribution of aftershocks. However, testing the different hypotheses is challenging because it requires the consideration of the large uncertainties involved in stress calculations as well as the appropriate consideration of secondary aftershock triggering which is related to stress changes induced by smaller pre- and aftershocks. In order to evaluate the forecast capability of different mechanisms, I take the effect of smaller--magnitude earthquakes into account by using the epidemic type aftershock sequence (ETAS) model where the spatial probability distribution of direct aftershocks, if available, is correlated to alternative source information and mechanisms. Surface shaking, rupture geometry, and slip distributions are tested. As an approximation of the shaking level, ShakeMaps are used which are available in near real-time after a mainshock and thus could be used for first-order forecasts of the spatial aftershock distribution. Alternatively, the use of empirical decay laws related to minimum fault distance is tested and Coulomb stress change calculations based on published and random slip models. For comparison, the likelihood values of the different model combinations are analyzed in the case of several well-known aftershock sequences (1992 Landers, 1999 Hector Mine, 2004 Parkfield). The tests show that the fault geometry is the most valuable information for improving aftershock forecasts. Furthermore, they reveal that static stress maps can additionally improve the forecasts of off--fault aftershock locations, while the integration of ground shaking data could not upgrade the results significantly. In the second part of this work, I focused on a procedure to test the information content of inverted slip models. This allows to quantify the information gain if this kind of data is included in aftershock forecasts. For this purpose, the ETAS model based on static stress changes, which is introduced in part one, is applied. The forecast ability of the models is systematically tested for several earthquake sequences and compared to models using random slip distributions. The influence of subfault resolution and segment strike and dip is tested. Some of the tested slip models perform very good, in that cases almost no random slip models are found to perform better. Contrastingly, for some of the published slip models, almost all random slip models perform better than the published slip model. Choosing a different subfault resolution hardly influences the result, as long the general slip pattern is still reproducible. Whereas different strike and dip values strongly influence the results depending on the standard deviation chosen, which is applied in the process of randomly selecting the strike and dip values.}, language = {en} } @phdthesis{Bathke2014, author = {Bathke, Hannes}, title = {An investigation of complex deformation patterns detected by using InSAR at Llaima and Tend{\"u}rek volcanoes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70522}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {Surface displacement at volcanic edifices is related to subsurface processes associated with magma movements, fluid transfers within the volcano edifice and gravity-driven deformation processes. Understanding of associated ground displacements is of importance for assessment of volcanic hazards. For example, volcanic unrest is often preceded by surface uplift, caused by magma intrusion and followed by subsidence, after the withdrawal of magma. Continuous monitoring of the surface displacement at volcanoes therefore might allow the forecasting of upcoming eruptions to some extent. In geophysics, the measured surface displacements allow the parameters of possible deformation sources to be estimated through analytical or numerical modeling. This is one way to improve the understanding of subsurface processes acting at volcanoes. Although the monitoring of volcanoes has significantly improved in the last decades (in terms of technical advancements and number of monitored volcanoes), the forecasting of volcanic eruptions remains puzzling. In this work I contribute towards the understanding of the subsurface processes at volcanoes and thus to the improvement of volcano eruption forecasting. I have investigated the displacement field of Llaima volcano in Chile and of Tend{\"u}rek volcano in East Turkey by using synthetic aperture radar interferometry (InSAR). Through modeling of the deformation sources with the extracted displacement data, it was possible to gain insights into potential subsurface processes occurring at these two volcanoes that had been barely studied before. The two volcanoes, although of very different origin, composition and geometry, both show a complexity of interacting deformation sources. At Llaima volcano, the InSAR technique was difficult to apply, due to the large decorrelation of the radar signal between the acquisition of images. I developed a model-based unwrapping scheme, which allows the production of reliable displacement maps at the volcano that I used for deformation source modeling. The modeling results show significant differences in pre- and post-eruptive magmatic deformation source parameters. Therefore, I conjecture that two magma chambers exist below Llaima volcano: a post-eruptive deep one and a shallow one possibly due to the pre-eruptive ascent of magma. Similar reservoir depths at Llaima have been confirmed by independent petrologic studies. These reservoirs are interpreted to be temporally coupled. At Tend{\"u}rek volcano I have found long-term subsidence of the volcanic edifice, which can be described by a large, magmatic, sill-like source that is subject to cooling contraction. The displacement data in conjunction with high-resolution optical images, however, reveal arcuate fractures at the eastern and western flank of the volcano. These are most likely the surface expressions of concentric ring-faults around the volcanic edifice that show low magnitudes of slip over a long time. This might be an alternative mechanism for the development of large caldera structures, which are so far assumed to be generated during large catastrophic collapse events. To investigate the potential subsurface geometry and relation of the two proposed interacting sources at Tend{\"u}rek, a sill-like magmatic source and ring-faults, I have performed a more sophisticated numerical modeling approach. The optimum source geometries show, that the size of the sill-like source was overestimated in the simple models and that it is difficult to determine the dip angle of the ring-faults with surface displacement data only. However, considering physical and geological criteria a combination of outward-dipping reverse faults in the west and inward-dipping normal faults in the east seem to be the most likely. Consequently, the underground structure at the Tend{\"u}rek volcano consists of a small, sill-like, contracting, magmatic source below the western summit crater that causes a trapdoor-like faulting along the ring-faults around the volcanic edifice. Therefore, the magmatic source and the ring-faults are also interpreted to be temporally coupled. In addition, a method for data reduction has been improved. The modeling of subsurface deformation sources requires only a relatively small number of well distributed InSAR observations at the earth's surface. Satellite radar images, however, consist of several millions of these observations. Therefore, the large amount of data needs to be reduced by several orders of magnitude for source modeling, to save computation time and increase model flexibility. I have introduced a model-based subsampling approach in particular for heterogeneously-distributed observations. It allows a fast calculation of the data error variance-covariance matrix, also supports the modeling of time dependent displacement data and is, therefore, an alternative to existing methods.}, language = {en} } @phdthesis{Nikolaeva2013, author = {Nikolaeva, Elena}, title = {Landslide kinematics and interactions studied in central Georgia by using synthetic aperture radar interferometry, optical imagery and inverse modeling}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70406}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Landslides are one of the biggest natural hazards in Georgia, a mountainous country in the Caucasus. So far, no systematic monitoring and analysis of the dynamics of landslides in Georgia has been made. Especially as landslides are triggered by extrinsic processes, the analysis of landslides together with precipitation and earthquakes is challenging. In this thesis I describe the advantages and limits of remote sensing to detect and better understand the nature of landslide in Georgia. The thesis is written in a cumulative form, composing a general introduction, three manuscripts and a summary and outlook chapter. In the present work, I measure the surface displacement due to active landslides with different interferometric synthetic aperture radar (InSAR) methods. The slow landslides (several cm per year) are well detectable with two-pass interferometry. In same time, the extremely slow landslides (several mm per year) could be detected only with time series InSAR techniques. I exemplify the success of InSAR techniques by showing hitherto unknown landslides, located in the central part of Georgia. Both, the landslide extent and displacement rate is quantified. Further, to determine a possible depth and position of potential sliding planes, inverse models were developed. Inverse modeling searches for parameters of source which can create observed displacement distribution. I also empirically estimate the volume of the investigated landslide using displacement distributions as derived from InSAR combined with morphology from an aerial photography. I adapted a volume formula for our case, and also combined available seismicity and precipitation data to analyze potential triggering factors. A governing question was: What causes landslide acceleration as observed in the InSAR data? The investigated area (central Georgia) is seismically highly active. As an additional product of the InSAR data analysis, a deformation area associated with the 7th September Mw=6.0 earthquake was found. Evidences of surface ruptures directly associated with the earthquake could not be found in the field, however, during and after the earthquake new landslides were observed. The thesis highlights that deformation from InSAR may help to map area prone landslides triggering by earthquake, potentially providing a technique that is of relevance for country wide landslide monitoring, especially as new satellite sensors will emerge in the coming years.}, language = {en} } @phdthesis{Grigoli2014, author = {Grigoli, Francesco}, title = {Automated seismic event location by waveform coherence analysis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70329}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterised by low signal-to-noise ratio, such methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this thesis I developed a picking free automated method based on the Short-Term-Average/Long-Term-Average (STA/LTA) traces at different stations as observed data. I used the STA/LTA of several characteristic functions in order to increase the sensitiveness to the P wave and the S waves. For the P phases we use the STA/LTA traces of the vertical energy function, while for the S phases, we use the STA/LTA traces of the horizontal energy trace and then a more optimized characteristic function which is obtained using the principal component analysis technique. The orientation of the horizontal components can be retrieved by robust and linear approach of waveform comparison between stations within a network using seismic sources outside the network (chapter 2). To locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a three-dimensional grid we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial and temporal coordinates of the seismic event. Location uncertainties are then estimated by perturbing the STA/LTA parameters (i.e the length of both long and short time windows) and relocating each event several times. In order to test the location method I firstly applied it to a set of 200 synthetic events. Then we applied it to two different real datasets. A first one related to mining induced microseismicity in a coal mine in the northern Germany (chapter 3). In this case we successfully located 391 microseismic event with magnitude range between 0.5 and 2.0 Ml. To further validate the location method I compared the retrieved locations with those obtained by manual picking procedure. The second dataset consist in a pilot application performed in the Campania-Lucania region (southern Italy) using a 33 stations seismic network (Irpinia Seismic Network) with an aperture of about 150 km (chapter 4). We located 196 crustal earthquakes (depth < 20 km) with magnitude range 1.1 < Ml < 2.7. A subset of these locations were compared with accurate locations retrieved by a manual location procedure based on the use of a double difference technique. In both cases results indicate good agreement with manual locations. Moreover, the waveform stacking location method results noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals.}, language = {en} } @phdthesis{Mohr2013, author = {Mohr, Christian Heinrich}, title = {Hydrological and erosion responses to man-made and natural disturbances : insights from forested catchments in South-central Chile}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70146}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Logging and large earthquakes are disturbances that may significantly affect hydrological and erosional processes and process rates, although in decisively different ways. Despite numerous studies that have documented the impacts of both deforestation and earthquakes on water and sediment fluxes, a number of details regarding the timing and type of de- and reforestation; seismic impacts on subsurface water fluxes; or the overall geomorphic work involved have remained unresolved. The main objective of this thesis is to address these shortcomings and to better understand and compare the hydrological and erosional process responses to such natural and man-made disturbances. To this end, south-central Chile provides an excellent natural laboratory owing to its high seismicity and the ongoing conversion of land into highly productive plantation forests. In this dissertation I combine paired catchment experiments, data analysis techniques, and physics-based modelling to investigate: 1) the effect of plantation forests on water resources, 2) the source and sink behavior of timber harvest areas in terms of overland flow generation and sediment fluxes, 3) geomorphic work and its efficiency as a function of seasonal logging, 4) possible hydrologic responses of the saturated zone to the 2010 Maule earthquake and 5) responses of the vadose zone to this earthquake. Re 1) In order to quantify the hydrologic impact of plantation forests, it is fundamental to first establish their water balances. I show that tree species is not significant in this regard, i.e. Pinus radiata and Eucalyptus globulus do not trigger any decisive different hydrologic response. Instead, water consumption is more sensitive to soil-water supply for the local hydro-climatic conditions. Re 2) Contradictory opinions exist about whether timber harvest areas (THA) generate or capture overland flow and sediment. Although THAs contribute significantly to hydrology and sediment transport because of their spatial extent, little is known about the hydrological and erosional processes occurring on them. I show that THAs may act as both sources and sinks for overland flow, which in turn intensifies surface erosion. Above a rainfall intensity of ~20 mm/h, which corresponds to <10\% of all rainfall, THAs may generate runoff whereas below that threshold they remain sinks. The overall contribution of Hortonian runoff is thus secondary considering the local rainfall regime. The bulk of both runoff and sediment is generated by Dunne, saturation excess, overland flow. I also show that logging may increase infiltrability on THAs which may cause an initial decrease in streamflow followed by an increase after the groundwater storage has been refilled. Re 3) I present changes in frequency-magnitude distributions following seasonal logging by applying Quantile Regression Forests at hitherto unprecedented detail. It is clearly the season that controls the hydro-geomorphic work efficiency of clear cutting. Logging, particularly dry seasonal logging, caused a shift of work efficiency towards less flashy and mere but more frequent moderate rainfall-runoff events. The sediment transport is dominated by Dunne overland flow which is consistent with physics-based modelling using WASA-SED. Re 4) It is well accepted that earthquakes may affect hydrological processes in the saturated zone. Assuming such flow conditions, consolidation of saturated saprolitic material is one possible response. Consolidation raises the hydraulic gradients which may explain the observed increase in discharge following earthquakes. By doing so, squeezed water saturates the soil which in turn increases the water accessible for plant transpiration. Post-seismic enhanced transpiration is reflected in the intensification of diurnal cycling. Re 5) Assuming unsaturated conditions, I present the first evidence that the vadose zone may also respond to seismic waves by releasing pore water which in turn feeds groundwater reservoirs. By doing so, water tables along the valley bottoms are elevated thus providing additional water resources to the riparian vegetation. By inverse modelling, the transient increase in transpiration is found to be 30-60\%. Based on the data available, both hypotheses, are not testable. Finally, when comparing the hydrological and erosional effects of the Maule earthquake with the impact of planting exotic plantation forests, the overall observed earthquake effects are comparably small, and limited to short time scales.}, language = {en} } @phdthesis{Buchhorn2013, author = {Buchhorn, Marcel}, title = {Ground-based hyperspectral and spectro-directional reflectance characterization of Arctic tundra vegetation communities : field spectroscopy and field spectro-goniometry of Siberian and Alaskan tundra in preparation of the EnMAP satellite mission}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70189}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {The Arctic tundra, covering approx. 5.5 \% of the Earth's land surface, is one of the last ecosystems remaining closest to its untouched condition. Remote sensing is able to provide information at regular time intervals and large spatial scales on the structure and function of Arctic ecosystems. But almost all natural surfaces reveal individual anisotropic reflectance behaviors, which can be described by the bidirectional reflectance distribution function (BRDF). This effect can cause significant changes in the measured surface reflectance depending on solar illumination and sensor viewing geometries. The aim of this thesis is the hyperspectral and spectro-directional reflectance characterization of important Arctic tundra vegetation communities at representative Siberian and Alaskan tundra sites as basis for the extraction of vegetation parameters, and the normalization of BRDF effects in off-nadir and multi-temporal remote sensing data. Moreover, in preparation for the upcoming German EnMAP (Environmental Mapping and Analysis Program) satellite mission, the understanding of BRDF effects in Arctic tundra is essential for the retrieval of high quality, consistent and therefore comparable datasets. The research in this doctoral thesis is based on field spectroscopic and field spectro-goniometric investigations of representative Siberian and Alaskan measurement grids. The first objective of this thesis was the development of a lightweight, transportable, and easily managed field spectro-goniometer system which nevertheless provides reliable spectro-directional data. I developed the Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS). The outcome of the field spectro-radiometrical measurements at the Low Arctic study sites along important environmental gradients (regional climate, soil pH, toposequence, and soil moisture) show that the different plant communities can be distinguished by their nadir-view reflectance spectra. The results especially reveal separation possibilities between the different tundra vegetation communities in the visible (VIS) blue and red wavelength regions. Additionally, the near-infrared (NIR) shoulder and NIR reflectance plateau, despite their relatively low values due to the low structure of tundra vegetation, are still valuable information sources and can separate communities according to their biomass and vegetation structure. In general, all different tundra plant communities show: (i) low maximum NIR reflectance; (ii) a weakly or nonexistent visible green reflectance peak in the VIS spectrum; (iii) a narrow "red-edge" region between the red and NIR wavelength regions; and (iv) no distinct NIR reflectance plateau. These common nadir-view reflectance characteristics are essential for the understanding of the variability of BRDF effects in Arctic tundra. None of the analyzed tundra communities showed an even closely isotropic reflectance behavior. In general, tundra vegetation communities: (i) usually show the highest BRDF effects in the solar principal plane; (ii) usually show the reflectance maximum in the backward viewing directions, and the reflectance minimum in the nadir to forward viewing directions; (iii) usually have a higher degree of reflectance anisotropy in the VIS wavelength region than in the NIR wavelength region; and (iv) show a more bowl-shaped reflectance distribution in longer wavelength bands (>700 nm). The results of the analysis of the influence of high sun zenith angles on the reflectance anisotropy show that with increasing sun zenith angles, the reflectance anisotropy changes to azimuthally symmetrical, bowl-shaped reflectance distributions with the lowest reflectance values in the nadir view position. The spectro-directional analyses also show that remote sensing products such as the NDVI or relative absorption depth products are strongly influenced by BRDF effects, and that the anisotropic characteristics of the remote sensing products can significantly differ from the observed BRDF effects in the original reflectance data. But the results further show that the NDVI can minimize view angle effects relative to the contrary spectro-directional effects in the red and NIR bands. For the researched tundra plant communities, the overall difference of the off-nadir NDVI values compared to the nadir value increases with increasing sensor viewing angles, but on average never exceeds 10 \%. In conclusion, this study shows that changes in the illumination-target-viewing geometry directly lead to an altering of the reflectance spectra of Arctic tundra communities according to their object-specific BRDFs. Since the different tundra communities show only small, but nonetheless significant differences in the surface reflectance, it is important to include spectro-directional reflectance characteristics in the algorithm development for remote sensing products.}, language = {en} } @phdthesis{Vogel2013, author = {Vogel, Kristin}, title = {Applications of Bayesian networks in natural hazard assessments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69777}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Even though quite different in occurrence and consequences, from a modeling perspective many natural hazards share similar properties and challenges. Their complex nature as well as lacking knowledge about their driving forces and potential effects make their analysis demanding: uncertainty about the modeling framework, inaccurate or incomplete event observations and the intrinsic randomness of the natural phenomenon add up to different interacting layers of uncertainty, which require a careful handling. Nevertheless deterministic approaches are still widely used in natural hazard assessments, holding the risk of underestimating the hazard with disastrous effects. The all-round probabilistic framework of Bayesian networks constitutes an attractive alternative. In contrast to deterministic proceedings, it treats response variables as well as explanatory variables as random variables making no difference between input and output variables. Using a graphical representation Bayesian networks encode the dependency relations between the variables in a directed acyclic graph: variables are represented as nodes and (in-)dependencies between variables as (missing) edges between the nodes. The joint distribution of all variables can thus be described by decomposing it, according to the depicted independences, into a product of local conditional probability distributions, which are defined by the parameters of the Bayesian network. In the framework of this thesis the Bayesian network approach is applied to different natural hazard domains (i.e. seismic hazard, flood damage and landslide assessments). Learning the network structure and parameters from data, Bayesian networks reveal relevant dependency relations between the included variables and help to gain knowledge about the underlying processes. The problem of Bayesian network learning is cast in a Bayesian framework, considering the network structure and parameters as random variables itself and searching for the most likely combination of both, which corresponds to the maximum a posteriori (MAP score) of their joint distribution given the observed data. Although well studied in theory the learning of Bayesian networks based on real-world data is usually not straight forward and requires an adoption of existing algorithms. Typically arising problems are the handling of continuous variables, incomplete observations and the interaction of both. Working with continuous distributions requires assumptions about the allowed families of distributions. To "let the data speak" and avoid wrong assumptions, continuous variables are instead discretized here, thus allowing for a completely data-driven and distribution-free learning. An extension of the MAP score, considering the discretization as random variable as well, is developed for an automatic multivariate discretization, that takes interactions between the variables into account. The discretization process is nested into the network learning and requires several iterations. Having to face incomplete observations on top, this may pose a computational burden. Iterative proceedings for missing value estimation become quickly infeasible. A more efficient albeit approximate method is used instead, estimating the missing values based only on the observations of variables directly interacting with the missing variable. Moreover natural hazard assessments often have a primary interest in a certain target variable. The discretization learned for this variable does not always have the required resolution for a good prediction performance. Finer resolutions for (conditional) continuous distributions are achieved with continuous approximations subsequent to the Bayesian network learning, using kernel density estimations or mixtures of truncated exponential functions. All our proceedings are completely data-driven. We thus avoid assumptions that require expert knowledge and instead provide domain independent solutions, that are applicable not only in other natural hazard assessments, but in a variety of domains struggling with uncertainties.}, language = {en} } @phdthesis{Schuetz2013, author = {Sch{\"u}tz, Felina}, title = {Surface heat flow and lithospheric thermal structure of the northwestern Arabian Plate}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69622}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {The surface heat flow (qs) is paramount for modeling the thermal structure of the lithosphere. Changes in the qs over a distinct lithospheric unit are normally directly reflecting changes in the crustal composition and therewith the radiogenic heat budget (e.g., Rudnick et al., 1998; F{\"o}rster and F{\"o}rster, 2000; Mareschal and Jaupart, 2004; Perry et al., 2006; Hasterok and Chapman, 2011, and references therein) or, less usual, changes in the mantle heat flow (e.g., Pollack and Chapman, 1977). Knowledge of this physical property is therefore of great interest for both academic research and the energy industry. The present study focuses on the qs of central and southern Israel as part of the Sinai Microplate (SM). Having formed during Oligocene to Miocene rifting and break-up of the African and Arabian plates, the SM is characterized by a young and complex tectonic history. Resulting from the time thermal diffusion needs to pass through the lithosphere, on the order of several tens-of-millions of years (e.g., Fowler, 1990); qs-values of the area reflect conditions of pre-Oligocene times. The thermal structure of the lithosphere beneath the SM in general, and south-central Israel in particular, has remained poorly understood. To address this problem, the two parameters needed for the qs determination were investigated. Temperature measurements were made at ten pre-existing oil and water exploration wells, and the thermal conductivity of 240 drill core and outcrop samples was measured in the lab. The thermal conductivity is the sensitive parameter in this determination. Lab measurements were performed on both, dry and water-saturated samples, which is labor- and time-consuming. Another possibility is the measurement of thermal conductivity in dry state and the conversion to a saturated value by using mean model approaches. The availability of a voluminous and diverse dataset of thermal conductivity values in this study allowed (1) in connection with the temperature gradient to calculate new reliable qs values and to use them to model the thermal pattern of the crust in south-central Israel, prior to young tectonic events, and (2) in connection with comparable datasets, controlling the quality of different mean model approaches for indirect determination of bulk thermal conductivity (BTC) of rocks. The reliability of numerically derived BTC values appears to vary between different mean models, and is also strongly dependent upon sample lithology. Yet, correction algorithms may significantly reduce the mismatch between measured and calculated conductivity values based on the different mean models. Furthermore, the dataset allowed the derivation of lithotype-specific conversion equations to calculate the water-saturated BTC directly from data of dry-measured BTC and porosity (e.g., well log derived porosity) with no use of any mean model and thus provide a suitable tool for fast analysis of large datasets. The results of the study indicate that the qs in the study area is significantly higher than previously assumed. The new presented qs values range between 50 and 62 mW m⁻². A weak trend of decreasing heat flow can be identified from the east to the west (55-50 mW m⁻²), and an increase from the Dead Sea Basin to the south (55-62 mW m⁻²). The observed range can be explained by variation in the composition (heat production) of the upper crust, accompanied by more systematic spatial changes in its thickness. The new qs data then can be used, in conjunction with petrophysical data and information on the structure and composition of the lithosphere, to adjust a model of the pre-Oligocene thermal state of the crust in south-central Israel. The 2-D steady-state temperature model was calculated along an E-W traverse based on the DESIRE seismic profile (Mechie et al., 2009). The model comprises the entire lithosphere down to the lithosphere-asthenosphere boundary (LAB) involving the most recent knowledge of the lithosphere in pre-Oligocene time, i.e., prior to the onset of rifting and plume-related lithospheric thermal perturbations. The adjustment of modeled and measured qs allows conclusions about the pre-Oligocene LAB-depth. After the best fitting the most likely depth is 150 km which is consistent with estimations made in comparable regions of the Arabian Shield. It therefore comprises the first ever modelled pre-Oligocene LAB depth, and provides important clues on the thermal state of lithosphere before rifting. This, in turn, is vital for a better understanding of the (thermo)-dynamic processes associated with lithosphere extension and continental break-up.}, language = {en} } @phdthesis{RiveraVillarreyes2013, author = {Rivera Villarreyes, Carlos Andres}, title = {Cosmic-ray neutron sensing for soil moisture measurements in cropped fields}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69748}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {This cumulative dissertation explored the use of the detection of natural background of fast neutrons, the so-called cosmic-ray neutron sensing (CRS) approach to measure field-scale soil moisture in cropped fields. Primary cosmic rays penetrate the top atmosphere and interact with atmospheric particles. Such interaction results on a cascade of high-energy neutrons, which continue traveling through the atmospheric column. Finally, neutrons penetrate the soil surface and a second cascade is produced with the so-called secondary cosmic-ray neutrons (fast neutrons). Partly, fast neutrons are absorbed by hydrogen (soil moisture). Remaining neutrons scatter back to the atmosphere, where its flux is inversely correlated to the soil moisture content, therefore allowing a non-invasive indirect measurement of soil moisture. The CRS methodology is mainly evaluated based on a field study carried out on a farmland in Potsdam (Brandenburg, Germany) along three crop seasons with corn, sunflower and winter rye; a bare soil period; and two winter periods. Also, field monitoring was carried out in the Schaefertal catchment (Harz, Germany) for long-term testing of CRS against ancillary data. In the first experimental site, the CRS method was calibrated and validated using different approaches of soil moisture measurements. In a period with corn, soil moisture measurement at the local scale was performed at near-surface only, and in subsequent periods (sunflower and winter rye) sensors were placed in three depths (5 cm, 20 cm and 40 cm). The direct transfer of CRS calibration parameters between two vegetation periods led to a large overestimation of soil moisture by the CRS. Part of this soil moisture overestimation was attributed to an underestimation of the CRS observation depth during the corn period ( 5-10 cm), which was later recalculated to values between 20-40 cm in other crop periods (sunflower and winter rye). According to results from these monitoring periods with different crops, vegetation played an important role on the CRS measurements. Water contained also in crop biomass, above and below ground, produces important neutron moderation. This effect was accounted for by a simple model for neutron corrections due to vegetation. It followed crop development and reduced overall CRS soil moisture error for periods of sunflower and winter rye. In Potsdam farmland also inversely-estimated soil hydraulic parameters were determined at the field scale, using CRS soil moisture from the sunflower period. A modelling framework coupling HYDRUS-1D and PEST was applied. Subsequently, field-scale soil hydraulic properties were compared against local scale soil properties (modelling and measurements). Successful results were obtained here, despite large difference in support volume. Simple modelling framework emphasizes future research directions with CRS soil moisture to parameterize field scale models. In Schaefertal catchment, CRS measurements were verified using precipitation and evapotranspiration data. At the monthly resolution, CRS soil water storage was well correlated to these two weather variables. Also clearly, water balance could not be closed due to missing information from other compartments such as groundwater, catchment discharge, etc. In the catchment, the snow influence to natural neutrons was also evaluated. As also observed in Potsdam farmland, CRS signal was strongly influenced by snow fall and snow accumulation. A simple strategy to measure snow was presented for Schaefertal case. Concluding remarks of this dissertation showed that (a) the cosmic-ray neutron sensing (CRS) has a strong potential to provide feasible measurement of mean soil moisture at the field scale in cropped fields; (b) CRS soil moisture is strongly influenced by other environmental water pools such as vegetation and snow, therefore these should be considered in analysis; (c) CRS water storage can be used for soil hydrology modelling for determination of soil hydraulic parameters; and (d) CRS approach has strong potential for long term monitoring of soil moisture and for addressing studies of water balance.}, language = {en} }