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- Institut für Geowissenschaften (508) (remove)
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.
Soil conditions under vegetation cover and their spatial and temporal variations from point to catchment scale are crucial for understanding hydrological processes within the vadose zone, for managing irrigation and consequently maximizing yield by precision farming. Soil moisture and soil roughness are the key parameters that characterize the soil status. In order to monitor their spatial and temporal variability on large scales, remote sensing techniques are required. Therefore the determination of soil parameters under vegetation cover was approached in this thesis by means of (multi-angular) polarimetric SAR acquisitions at a longer wavelength (L-band, lambda=23cm). In this thesis, the penetration capabilities of L-band are combined with newly developed (multi-angular) polarimetric decomposition techniques to separate the different scattering contributions, which are occurring in vegetation and on ground. Subsequently the ground components are inverted to estimate the soil characteristics. The novel (multi-angular) polarimetric decomposition techniques for soil parameter retrieval are physically-based, computationally inexpensive and can be solved analytically without any a priori knowledge. Therefore they can be applied without test site calibration directly to agricultural areas. The developed algorithms are validated with fully polarimetric SAR data acquired by the airborne E-SAR sensor of the German Aerospace Center (DLR) for three different study areas in Germany. The achieved results reveal inversion rates up to 99% for the soil moisture and soil roughness retrieval in agricultural areas. However, in forested areas the inversion rate drops significantly for most of the algorithms, because the inversion in forests is invalid for the applied scattering models at L-band. The validation against simultaneously acquired field measurements indicates an estimation accuracy (root mean square error) of 5-10vol.% for the soil moisture (range of in situ values: 1-46vol.%) and of 0.37-0.45cm for the soil roughness (range of in situ values: 0.5-4.0cm) within the catchment. Hence, a continuous monitoring of soil parameters with the obtained precision, excluding frozen and snow covered conditions, is possible. Especially future, fully polarimetric, space-borne, long wavelength SAR missions can profit distinctively from the developed polarimetric decomposition techniques for separation of ground and volume contributions as well as for soil parameter retrieval on large spatial scales.
Soil moisture is a key state variable that controls runoff formation, infiltration and partitioning of radiation into latent and sensible heat. However, the experimental characterisation of near surface soil moisture patterns and their controls on runoff formation remains a challenge. This subject was one aspect of the BMBF-funded OPAQUE project (operational discharge and flooding predictions in head catchments). As part of that project the focus of this dissertation is on: (1) testing the methodology and feasibility of the Spatial TDR technology in producing soil moisture profiles along TDR probes, including an inversion technique of the recorded signal in heterogeneous field soils, (2) the analysis of spatial variability and temporal dynamics of soil moisture at the field scale including field experiments and hydrological modelling, (3) the application of models of different complexity for understanding soil moisture dynamics and its importance for runoff generation as well as for improving the prediction of runoff volumes. To fulfil objective 1, several laboratory experiments were conducted to understand the influence of probe rod geometry and heterogeneities in the sampling volume under different wetness conditions. This includes a detailed analysis on how these error sources affect retrieval of soil moisture profiles in soils. Concerning objective 2 a sampling strategy of two TDR clusters installed in the head water of the Wilde Weißeritz catchment (Eastern Ore Mountains, Germany) was used to investigate how well “the catchment state” can be characterised by means of distributed soil moisture data observed at the field scale. A grassland site and a forested site both located on gentle slopes were instrumented with two Spatial TDR clusters that consist of up to 39 TDR probes. Process understanding was gained by modelling the interaction of evapotranspiration and soil moisture with the hydrological process model CATFLOW. A field scale irrigation experiment was carried out to investigate near subsurface processes at the hillslope scale. The interactions of soil moisture and runoff formation were analysed using discharge data from three nested catchments: the Becherbach with a size of 2 km², the Rehefeld catchment (17 km²) and the superordinate Ammelsdorf catchment (49 km²). Statistical analyses including observations of pre-event runoff, soil moisture and different rainfall characteristics were employed to predict stream flow volume. On the different scales a strong correlation between the average soil moisture and the runoff coefficients of rainfall-runoff events could be found, which almost explains equivalent variability as the pre-event runoff. Furthermore, there was a strong correlation between surface soil moisture and subsurface wetness with a hysteretic behaviour between runoff soil moisture. To fulfil objective 3 these findings were used in a generalised linear model (GLM) analysis which combines state variables describing the catchments antecedent wetness and variables describing the meteorological forcing in order to predict event runoff coefficients. GLM results were compared to simulations with the catchment model WaSiM ETH. Hereby were the model results of the GLMs always better than the simulations with WaSiM ETH. The GLM analysis indicated that the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore soil moisture controls on runoff generation and can be an important link between the scales. Long term monitoring of such sites could yield valuable information for flood warning and forecasting by identifying critical soil moisture conditions for the former and providing a better representation of the initial moisture conditions for the latter.
Major challenges during geothermal exploration and exploitation include the structural-geological characterization of the geothermal system and the application of sustainable monitoring concepts to explain changes in a geothermal reservoir during production and/or reinjection of fluids. In the absence of sufficiently permeable reservoir rocks, faults and fracture networks are preferred drilling targets because they can facilitate the migration of hot and/or cold fluids. In volcanic-geothermal systems considerable amounts of gas emissions can be released at the earth surface, often related to these fluid-releasing structures.
In this thesis, I developed and evaluated different methodological approaches and measurement concepts to determine the spatial and temporal variation of several soil gas parameters to understand the structural control on fluid flow. In order to validate their potential as innovative geothermal exploration and monitoring tools, these methodological approaches were applied to three different volcanic-geothermal systems. At each site an individual survey design was developed regarding the site-specific questions.
The first study presents results of the combined measurement of CO2 flux, ground temperatures, and the analysis of isotope ratios (δ13CCO2, 3He/4He) across the main production area of the Los Humeros geothermal field, to identify locations with a connection to its supercritical (T > 374◦C and P > 221 bar) geothermal reservoir. The results of the systematic and large-scale (25 x 200 m) CO2 flux scouting survey proved to be a fast and flexible way to identify areas of anomalous degassing. Subsequent sampling with high resolution surveys revealed the actual extent and heterogenous pattern of anomalous degassing areas. They have been related to the internal fault hydraulic architecture and allowed to assess favourable structural settings for fluid flow such as fault intersections. Finally, areas of unknown structurally controlled permeability with a connection to the superhot geothermal reservoir have been determined, which represent promising targets for future geothermal exploration and development.
In the second study, I introduce a novel monitoring approach by examining the variation of CO2 flux to monitor changes in the reservoir induced by fluid reinjection. For that reason, an automated, multi-chamber CO2 flux system was deployed across the damage zone of a major normal fault crossing the Los Humeros geothermal field. Based on the results of the CO2 flux scouting survey, a suitable site was selected that had a connection to the geothermal reservoir, as identified by hydrothermal CO2 degassing and hot ground temperatures (> 50 °C). The results revealed a response of gas emissions to changes in reinjection rates within 24 h, proving an active hydraulic communication between the geothermal reservoir and the earth surface. This is a promising monitoring strategy that provides nearly real-time and in-situ data about changes in the reservoir and allows to timely react to unwanted changes (e.g., pressure decline, seismicity).
The third study presents results from the Aluto geothermal field in Ethiopia where an area-wide and multi-parameter analysis, consisting of measurements of CO2 flux, 222Rn, and 220Rn activity concentrations and ground temperatures was conducted to detect hidden permeable structures. 222Rn and 220Rn activity concentrations are evaluated as a complementary soil gas parameter to CO2 flux, to investigate their potential to understand tectono-volcanic degassing. The combined measurement of all parameters enabled to develop soil gas fingerprints, a novel visualization approach. Depending on the magnitude of gas emissions and their migration velocities the study area was divided in volcanic (heat), tectonic (structures), and volcano-tectonic dominated areas. Based on these concepts, volcano-tectonic dominated areas, where hot hydrothermal fluids migrate along permeable faults, present the most promising targets for future geothermal exploration and development in this geothermal field. Two of these areas have been identified in the south and south-east which have not yet been targeted for geothermal exploitation. Furthermore, two unknown areas of structural related permeability could be identified by 222Rn and 220Rn activity concentrations.
Eventually, the fourth study presents a novel measurement approach to detect structural controlled CO2 degassing, in Ngapouri geothermal area, New Zealand. For the first time, the tunable diode laser (TDL) method was applied in a low-degassing geothermal area, to evaluate its potential as a geothermal exploration method. Although the sampling approach is based on profile measurements, which leads to low spatial resolution, the results showed a link between known/inferred faults and increased CO2 concentrations. Thus, the TDL method proved to be a successful in the determination of structural related permeability, also in areas where no obvious geothermal activity is present. Once an area of anomalous CO2 concentrations has been identified, it can be easily complemented by CO2 flux grid measurements to determine the extent and orientation of the degassing segment.
With the results of this work, I was able to demonstrate the applicability of systematic and area-wide soil gas measurements for geothermal exploration and monitoring purposes. In particular, the combination of different soil gases using different measurement networks enables the identification and characterization of fluid-bearing structures and has not yet been used and/or tested as standard practice. The different studies present efficient and cost-effective workflows and demonstrate a hands-on approach to a successful and sustainable exploration and monitoring of geothermal resources. This minimizes the resource risk during geothermal project development. Finally, to advance the understanding of the complex structure and dynamics of geothermal systems, a combination of comprehensive and cutting-edge geological, geochemical, and geophysical exploration methods is essential.
In dieser Arbeit wird das regionale Klimamodell HIRHAM mit einer horizontalen Auflösung von 50 km und 19 vertikalen Schichten erstmals auf den asiatischen Kontinent angewendet, um die indische Monsunzirkulation unter rezenten und paläoklimatischen Bedingungen zu simulieren. Das Integrationsgebiet des Modells erstreckt sich von etwa 0ºN - 50ºN und 42ºE - 110ºE und bedeckt dabei sowohl die hohe Topographie des Himalajas und Tibet Plateaus als auch den nördlichen Indischen Ozean. Das Ziel besteht in der Beschreibung der regionalen Kopplung zwischen der Monsunzirkulation und den orographischen sowie diabatischen Antriebsmechanismen. Eine 44-jährige Modellsimulation von 1958-2001, die am seitlichen und unteren Rand von ECMWF Reanalysen (ERA40) angetrieben wird, bildet die Grundlage für die Validierung der Modellergebnisse mit Beobachtungen auf der Basis von Stations- und Gitterdatensätzen. Der Fokus liegt dabei auf der atmosphärischen Zirkulation, der Temperatur und dem Niederschlag im Sommer- und Wintermonsun, wobei die Qualität des Modells sowohl in Bezug zur langfristigen und dekadischen Klimatologie als auch zur interannuellen Variabilität evaluiert wird. Im Zusammenhang mit einer realistischen Reproduktion der Modelltopographie kann für die Muster der Zirkulation und Temperatur eine gute Übereinstimmung zwischen Modell und Daten nachgewiesen werden. Der simulierte Niederschlag zeigt eine bessere Übereinstimmung mit einem hoch aufgelösten Gitterdatensatz über der Landoberfläche Zentralindiens und in den Hochgebirgsregionen, der den Vorteil des Regionalmodells gegenüber der antreibenden Reanalyse hervorhebt. In verschiedenen Fall- und Sensitivitätsstudien werden die wesentlichen Antriebsfaktoren des indischen Monsuns (Meeresoberflächentemperaturen, Stärke des winterlichen Sibirischen Hochs und Anomalien der Bodenfeuchte) untersucht. Die Ergebnisse machen deutlich, dass die Simulation dieser Mechanismen auch mit einem Regionalmodell sehr schwierig ist, da die Komplexität des Monsunsystems hochgradig nichtlinear ist und die vor allem subgridskalig wirkenden Prozesse im Modell noch nicht ausreichend parametrisiert und verstanden sind. Ein paläoklimatisches Experiment für eine 44-jährige Zeitscheibe im mittleren Holozän (etwa 6000 Jahre vor heute), die am Rand von einer globalen ECHAM5 Simulation angetrieben wird, zeigt markante Veränderungen in der Intensität des Monsuns durch die unterschiedliche solare Einstrahlung, die wiederum Einflüsse auf die SST, die Zirkulation und damit auf die Niederschlagsmuster hat.
Signals stored in sediment
(2018)
Tectonic and climatic boundary conditions determine the amount and the characteristics (size distribution and composition) of sediment that is generated and exported from mountain regions. On millennial timescales, rivers adjust their morphology such that the incoming sediment (Qs,in) can be transported downstream by the available water discharge (Qw). Changes in climatic and tectonic boundary conditions thus trigger an adjustment of the downstream river morphology. Understanding the sensitivity of river morphology to perturbations in boundary conditions is therefore of major importance, for example, for flood assessments, infrastructure and habitats. Although we have a general understanding of how rivers evolve over longer timescales, the prediction of channel response to changes in boundary conditions on a more local scale and over shorter timescales remains a major challenge. To better predict morphological channel evolution, we need to test (i) how channels respond to perturbations in boundary conditions and (ii) how signals reflecting the persisting conditions are preserved in sediment characteristics. This information can then be applied to reconstruct how local river systems have evolved over time.
In this thesis, I address those questions by combining targeted field data collection in the Quebrada del Toro (Southern Central Andes of NW Argentina) with cosmogenic nuclide analysis and remote sensing data. In particular, I (1) investigate how information on hillslope processes is preserved in the 10Be concentration (geochemical composition) of fluvial sediments and how those signals are altered during downstream transport. I complement the field-based approach with physical experiments in the laboratory, in which I (2) explore how changes in sediment supply (Qs,in) or water discharge (Qw) generate distinct signals in the amount of sediment discharge at the basin outlet (Qs,out). With the same set of experiments, I (3) study the adjustments of alluvial channel morphology to changes in Qw and Qs,in, with a particular focus in fill-terrace formation. I transfer the findings from the experiments to the field to (4) reconstruct the evolution of a several-hundred meter thick fluvial fill-terrace sequence in the Quebrada del Toro. I create a detailed terrace chronology and perform reconstructions of paleo-Qs and Qw from the terrace deposits. In the following paragraphs, I summarize my findings on each of these four topics.
First, I sampled detrital sediment at the outlet of tributaries and along the main stem in the Quebrada del Toro, analyzed their 10Be concentration ([10Be]) and compared the data to a detailed hillslope-process inventory. The often observed non-linear increase in catchment-mean denudation rate (inferred from [10Be] in fluvial sediment) with catchment-median slope, which has commonly been explained by an adjustment in landslide-frequency, coincided with a shift in the main type of hillslope processes. In addition, the [10Be] in fluvial sediments varied with grain-size. I defined the normalized sand-gravel-index (NSGI) as the 10Be-concentration difference between sand and gravel fractions divided by their summed concentrations. The NSGI increased with median catchment slope and coincided with a shift in the prevailing hillslope processes active in the catchments, thus making the NSGI a potential proxy for the evolution of hillslope processes over time from sedimentary deposits. However, the NSGI recorded hillslope-processes less well in regions of reduced hillslope-channel connectivity and, in addition, has the potential to be altered during downstream transport due to lateral sediment input, size-selective sediment transport and abrasion.
Second, my physical experiments revealed that sediment discharge at the basin outlet (Qs,out) varied in response to changes in Qs,in or Qw. While changes in Qw caused a distinct signal in Qs,out during the transient adjustment phase of the channel to new boundary conditions, signals related to changes in Qs,in were buffered during the transient phase and likely only become apparent once the channel is adjusted to the new conditions. The temporal buffering is related to the negative feedback between Qs,in and channel-slope adjustments. In addition, I inferred from this result that signals extracted from the geochemical composition of sediments (e.g., [10Be]) are more likely to represent modern-day conditions during times of aggradation, whereas the signal will be temporally buffered due to mixing with older, remobilized sediment during times of channel incision.
Third, the same set of experiments revealed that river incision, channel-width narrowing and terrace cutting were initiated by either an increase in Qw, a decrease in Qs,in or a drop in base level. The lag-time between the external perturbation and the terrace cutting determined (1) how well terrace surfaces preserved the channel profile prior to perturbation and (2) the degree of reworking of terrace-surface material. Short lag-times and well preserved profiles occurred in cases with a rapid onset of incision. Also, lag-times were synchronous along the entire channel after upstream perturbations (Qw, Qs,in), whereas base-level fall triggered an upstream migrating knickzone, such that lag-times increased with distance upstream. Terraces formed after upstream perturbations (Qw, Qs,in) were always steeper when compared to the active channel in new equilibrium conditions. In the base-level fall experiment, the slope of the terrace-surfaces and the modern channel were similar. Hence, slope comparisons between the terrace surface and the modern channel can give insights into the mechanism of terrace formation.
Fourth, my detailed terrace-formation chronology indicated that cut-and-fill episodes in the Quebrada del Toro followed a ~100-kyr cyclicity, with the oldest terraces ~ 500 kyr old. The terraces were formed due to variability in upstream Qw and Qs. Reconstructions of paleo-Qs over the last 500 kyr, which were restricted to times of sediment deposition, indicated only minor (up to four-fold) variations in paleo-denudation rates. Reconstructions of paleo-Qw were limited to the times around the onset of river incision and revealed enhanced discharge from 10 to 85% compared to today. Such increases in Qw are in agreement with other quantitative paleo-hydrological reconstructions from the Eastern Andes, but have the advantage of dating further back in time.
Selenite pseudomorphs
(2019)