ALBERT

Description: Elevated levels of arsenic (As) in soils and groundwaters remain a pressing global challenge due to its widespread occurrence and distribution, high toxicity and mobility. In oxygen-limited subsurface conditions, redox-active mineral phases can be important substrates in controlling the fate and mobility of As in the environment. Among these redox-active minerals, green rust (GR) phases, an Fe(II)-Fe(III)-bearing layered double hydroxide, have been shown to be able to sequester a wide range of toxic metals and metalloids, including As. However, very little is known regarding how GR phases interact with As species and what is the fate of the immobilized As under dynamic geochemical conditions. GR phases are suggested to form through the transformation of metastable iron mineral phases in non-sulfidic, reducing environments. However, the exact mechanism and pathway of this transformation, as well as the fate of mineral-associated As (i.e. whether it is re-released back into the groundwater by desorption, dissolution or redox transformation) is not yet known but critically needed for modelling As cycling in contaminated environments. To address these knowledge gaps, I conducted a series of experimental geochemical studies and combined them with various laboratory- and synchrotron-based solid and liquid phase characterization methods to examine the interaction between GR sulfate (GRSO4) and As species [As(III) and As(V)]. Specifically, I performed several batch experiments under anoxic and near-neutral pH conditions to determine As-GR interaction mechanisms during GR formation and transformation. Moreover, I also quantified how these transformation reactions affect the toxicity and mobility of As species in contaminated environments. From the batch adsorption experiments, I showed that synthetic GRSO4 can adsorb up to 160 and 105 mg of As(III) and As(V) per g of solid, respectively. These adsorption capacities are among the highest reported for iron (oxyhydr)oxides that form in soils and groundwaters. Results from this study also show that As removal by GRSO4 can be inhibited by several geochemical parameters such as pH, high ionic strength, presence of co-existing inorganic ions (e.g., Mg2+, PO43-, Si) and low temperature. I also employed an integrated nano-scale solid-state characterization approach to elucidate As-GRSO4 interactions. Specifically, I combined scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray (EDX) spectroscopy together with bulk synchrotron-based X-ray techniques including high energy X-ray total scattering, pair distribution function (PDF) analysis and X-ray absorption spectroscopy (XAS). With these, I was able to directly visualize and pinpoint As binding sites at the GR surface sites and to identify the binding mechanism for both As(III) and As(V). In the case of As(III)-reacted GR, STEM-EDX maps showed that As(III) were preferentially adsorbed at the GR crystal edges, primarily as bidentate binuclear (2C) inner-sphere surface complexes based from the differential PDF and As K-edge XAS data. For the As(V)-reacted GR, As(V) was sequestered as a newly-formed As-bearing mineral phase parasymplesite and as adsorbed As(V) species at the GR edges (in 2C geometry). To assess the fate of As in subsurface environments, I studied As during GR formation and transformation to quantify As uptake and/or its potential release back into solution and the stability of GR and other Fe (oxhydr)oxide phases in this process. During the Fe2+-induced transformation of As(V)-bearing ferrihydrite, I followed the changes in aqueous behavior and speciation of As, as well as the changes in composition of the Fe mineral phases, as a function of varying Fe2+(aq)/Fe(III)solid ratios (0.5, 1 ,2). In all the ratios tested, GRSO4, goethite and lepidocrocite formed in the early stages of transformation (≤ 2h). However, at low ratios (〈2), the initially formed GRSo4 and/or lepidocrocite disappeared as the reaction progressed, leaving goethite and unreacted ferrihydrite after 24 h. At an Fe2+(aq)/Fe(III)solid ratio of 2, GRSO4 was formed and remained in the solids until the end of the 24-h transformation, with goethite and unreacted ferrihydrite. The initial As(V) was partially reduced to As(III) by the surface-associated Fe2+-GT redox couple, and extent of reduction increased from 34 to 44% as Fe2+(aq)/Fe(III)solid ratios increased. Despite this reduction to the more mobile and more toxic As(III) species, no significant As release was observed during the mineral transformation reactions. Finally, I tested the long-term stability and reactivity of GR by aging synthetic GRSO4 in pristine and As-spiked natural groundwater at ambient (25 °C) and low (4 °C) temperatures. The spiked As in the groundwater was completely removed after 120 days at 25 °C while the removal rate was ~2 times slower at 4 °C with only ~66% As removal after 120 days. On the other hand, the stability of synthetic GRSO4 in groundwater was strongly affected by the presence of adsorbed As species and temperature. At ambient temperature, the initial GRSO4 aged in As-free groundwater was converted to GRCO3 by ion exchange within a few days and both GR phases eventually transformed to magnetite after 120 days. Remarkably, both the addition of As species in groundwater and lowering the temperature increased long-term GRSO4 stability through the inhibition of (a) ion exchange in the GRSO4 interlayer (i.e., slower conversion to GRCO3) and (b) transformation of GR to magnetite. Moreover, a synergistic stabilization effect was observed with both As addition and low temperature, significantly enhancing GR stability up to a year. Overall, the work presented in this thesis clearly emphasizes the potential role of GR phases in controlling the mobility and toxicity of As species in subsurface environments. Specifically, I contributed to the fundamental understanding of the reactions involving As(III) and As(V) at GR surfaces, elucidating the relevant binding mechanisms and visualizing specific binding sites of immobilized As species. This work also identified critical geochemical factors that affect As removal and GR formation and transformation under anoxic and circum-neutral pH conditions. More importantly, I was able to show the enhanced long-term stability of GR in natural groundwaters and its prolonged reactivity for As sequestration.

Description: Subduction zones are naturally complex systems, with much of their deformation being accommodated along the interface between two tectonic plates. Hence, the physical nature and the rheology of the subduction interface play an important role in the deformation, degree of locking, and slip processes during convergence, as well as large scale subduction dynamics.Over the last two decades, different slip patterns have been recognized by geodetic and seismic techniques, such as slow slip events and episodic tremor and slip, the physics behind which still evade us. Since direct observations along an active subduction interface are not feasible, field examples of exhumed zones can provide important insight into the nature of such transient events. Concurrently, most field outcrops suggest that the subduction interface is rather heterogeneous, comprising different units that deform following various patterns. However, these units are often too small to be resolved in a large-scale geodynamic model and are, therefore,not taken into account in such models. Outcrop-scale numerical experiments can be combined with natural structural observations from outcrops in order to refine the rheologies used in large geodynamic models. Here, methods ranging from field, petrological and geochronological observations on exhumed rocks to outcrop-scale numerical simulations are deployed, in order to investigate the rheology of the plate interface, the deformation mechanisms and the timing of deformation. The European Alps are a great natural laboratory exposing an almost continuous subduction interface allowing for the study of deformation processes from shallow to deeper segments (from ca. 10 km to ca. 45 km depth). Here, a network of fossil subduction plate interfaces preserved in the Central Alps (Val Malenco, N Italy) is used as a proxy to study such processes on subducting continental slices (the Margna and Sella nappes), at depths corresponding to the former brittle-ductile transition. This network of shear zones comprises mostly mylonites and schists but also rare foliated cataclasites, with different generations of micas and garnet locally overgrowing resorbed pre-Alpine cores. Thermodynamic modelling points to peak burial deformation conditions of ~0.9 GPa and 350°-400° C, at ca. 30 km depth. Rb/Sr geochronology on marbles yields an age of 48.9 ± 0.9 Ma, while a wide range of both Rb/Sr and 40Ar/39Ar apparent ages is obtained from deformed orthogneisses and micaschists embracing 87-44 Ma, due to incomplete recrystallization. Based on pressure-temperature, structural and geochronological observations, the studied shear zones last equilibrated at depths downdip of the seismogenic zone in an active subduction zone setting. Fluids contribute to the bulk rheology of this interface by enhancing pressure-solution creep which prevails in the microstructural record. This study suggests that this system of shear zones represents deformation conditions along the subduction interface(s) in the transition zone below the seismogenic zone during active subduction, where transient slip is found. Other exhumed subduction interfaces exhibit block-in-matrix characteristics, termed mélanges, the block concentration of which can affect their bulk rheology. To investigate this, synthetic models are created, with different proportions of strong blocks within a weak matrix, and compared to exhumed natural mélanges outcrops. 2D Finite Element visco-plastic models in simple shear are used to determine the effective rheological parameters of such a two-phase medium, comprising blocks of basalt within a wet quartzitic matrix. Models and their structures are treated as scale-independent and self-similar. Therefore, field geometries are upscaled to km-scale models, compatible with large-scale, geodetic and seismic observations. Outcrops of mélanges, as well as of other units deformed during subduction suggest that deformation is mainly taken up by dissolution-precipitation creep. However, flow laws for dissolution-precipitation creep are not well-established experimentally and scarcely used in large-scale numerical models. To make the results of this study comparable to and usable by numerical studies, dislocation creep is assumed to be the governing flow law for both phases (basalt and wet quartz). Finally, effective rheological estimates for a natural subduction interface are provided. The results suggest that block concentration affects deformation and strain localization, with the effective dislocation creep parameters (A, n, and Q) varying between the values of the strong and the weak phase, when both phases deform viscously. However, as the contribution of brittle deformation of the basaltic blocks increases, the value of the stress exponent, n, can exceed that of the purely strong phase. Using these effective parameters as input into seismic cycle models could help evaluate the possible effect of field heterogeneities on the slip behaviour of the plate interface. In summary, the heterogeneity of the subduction interface plays an important role in the degree of localization and rheology of the plate interface. Mixed brittle-ductile deformation is common in subducted rocks and might give rise to different kinematic behaviours. Re-assessing fabrics in exhumed rocks with respect to their (relevant) timing, spatial distribution, as well as cross-cutting relationships of individual fabric features is essential for linking kinematic far-field observations to the physics of deformation processes acting upon the interface. Finally, incorporating the results of small-scale numerical studies in large-scale geodynamic models may help improve our understanding of the mechanical behaviour of the plate interface, including transient or aseismic slip phenomena, which may control the recurrence of megathrust ruptures in active subduction systems.

Description: The study areas of this PhD thesis are located in the Peruvian and Argentinean Andean Back-Arc in South America. The thesis focuses on two major themes: firstly, on contractional thick-skinned tectonics (and related processes, regarding interplay and linkage of different structural styles); secondly, on multi-scale structural data integration and the quantification of uncertainty in kinematic restoration through forward modeling. Key scientific questions of this PhD thesis relate to the following: What controls the deformation styles in the Andean Back-Arc? How did the fractures in igneous rocks (hosted in thick-skinned structures) evolve in the greater tectonic context? How can uncertainty in kinematic restoration be quantified better? Data from numerous different sources was integrated and assessed. The data sources used herein, include 2D and 3D seismic data, well data, surface geology, satellite imagery, digital terrain data, earthquake focal mechanisms, drill core data and gravity-magnetics data. For the Santiago and Pachitea Basins (Peru), the analysis resulted in revised structural styles, improved structural architecture, new data on structural timing, new shortening amounts, new slip rates and an improved understanding of the interplay of different structural styles with particular emphasis on the impact of salt tectonics. For the Neuquén Basin (Argentina), a new evolutionary fracture model in oil producing igneous intrusions (sills), including improved reservoir characterization, was developed. For the Malargüe Anticline, also located in the Neuquén Basin, a novel workflow was developed, to quantify uncertainty quantification in kinematic restoration through forward modeling. In summary, highly variable tectonic response mechanisms are observed in the Andean Back-Arc. However, the impact of the mechanical stratigraphy appears to be more important and widespread than anticipated. Thick-skinned growth (with varying influence of salt tectonics) triggers thin-skinned thrusts. Alternating stress fields in the Back-Arc can explain complex fracture systems in brittle igneous rocks, where cooling fractures are overprinted by subsequent tectonic shearing motion. A newly developed forward modeling workflow allows for improved uncertainty quantification of thick-skinned contractional structures. This new workflow has various implications and should be tested by future researchers with various parameters simultaneously (e.g. through numerical modeling) and should be tested in other tectonic settings around the world, such as e.g. extensional or strike-slip settings.

Description: Extended nucleation phases of earthquakes have been regularly observed, yet the underlying mechanisms governing the initiation phase of rupture are yet to be understood in detail. Currently two end member models exist to explain earthquake nucleation: one model claiming that the nucleation phase of a small earthquake is indistinguishable from that of a large one, while the other proposes fundamental differences in the underlying process. Previous studies have been using the same seismological observations to argue for either model, leaving the need of further investigations into the nucleation behavior of earthquakes across scales and different settings. The thesis at hand contributes to the current discussion on earthquake nucleation by providing additional observational evidence for extended nucleation phases, complex rupture interaction and growth across a number of different scales and settings. Here, earthquake nucleation is investigated for three different scenarios, each with varying degrees of complexity: 1) the controlled case of induced seismicity in hydraulic stimulations of geothermal reservoirs, where rupture growth is assumed to be primarily governed by anthropogenic activity, 2) the partly-controlled setting of a geothermal field with a long history of fluid injection and production, and 3) the uncontrolled case of natural seismicity in the central Sea of Marmara, where earthquake nucleation is purely governed by the regional tectonics. First, the temporal evolution of seismicity and the growth of observed moment magnitudes for a range of past and present hydraulic stimulation projects associated with the creation of enhanced geothermal systems are analyzed. They reveal a clear linear relation between injected fluid volume/hydraulic energy and cumulative seismic moments. For most projects studied, the observations are in good agreement with existing physical models that predict a relation between injected fluid volume and maximum seismic moment of induced events. This suggests that seismicity results from a stable, pressure controlled rupture process at least for an extended injection period. Overall evolution of seismicity is independent of tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. In contrast, a few stimulations reveal unbound increase in seismic moment suggesting that for these cases evolution of seismicity is mainly controlled by stress field, the size of tectonic faults and fault connectivity. The uncertainty over whether or not a transition between behavior is likely to occur at any point during the injection is what motivates the need for a next generation monitoring and traffic-light system accounting for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution at high resolution for an immediate reaction in injection strategy. Furthermore, the majority of pressure-controlled stimulations shows the potential of actively controlling the size of induced earthquakes, if an injection protocol is chosen based on continuous feedback from a near-real-time seismic monitoring system. Second, moderate sized earthquakes at The Geysers geothermal field (California), where years of injection and production across hundreds of wells have led to a unique physical environment, are studied. While overall seismicity at The Geysers is generally governed by anthropogenic activities, contributions of individual wells or injection activities are hard to distinguish, thus making detailed managing of occurring magnitudes challenging. New high-resolution seismicity catalogs framing the occurrence of 20 ML 〉 2.5 earthquakes were created. The seismicity catalogs were developed using a matched filter algorithm, including automatic determination of P and S phase onsets and their inversion for absolute hypocenter locations with corresponding uncertainties. The selected 20 sequences sample different hypocentral depths and hydraulic conditions within the field. Seismic activity and magnitude frequency distributions displayed by the different earthquake sequences are correlated with their location within the reservoir. Sequences located in the northwestern part of the reservoir show overall increased seismic activity and low b values, while the southeastern part is dominated by decreased seismic activity and higher b values. Periods of high injection coincide with high b values and vice versa. These observations potentially reflect varying differential and mean stresses and damage of the reservoir rocks across the field. Additionally, a systematic search for seismicity localization using a multi-step cross-correlation analysis was performed. No evidence for increased correlation between the occurring seismicity and the mainshock for any of the 20 sequences could be seen, indicating that each main nucleation spot was seismically silent prior to the main rupture. However, a number of highly inter-correlated earthquakes for sequences below the reservoir and during high injection activity is observed. Under these conditions, the seismicity surrounding the future mainshock source region is more concentrated and might be evidence for a cascading nucleation process. About 50% of analyzed sequences exhibit no change in seismicity rate in response to the large main event. However, we find complex waveforms at the onset of the main earthquake, suggesting that small ruptures spontaneously grow into or trigger larger events, consistent with a cascading type nucleation. Third, the spatiotemporal evolution of seismicity during a sequence of moderate (MW4.7 and MW5.8) earthquakes occurring in September 2019 at the transition between a creeping and a locked segment of the North Anatolian Fault in the central Sea of Marmara (Turkey) was analyzed. A matched filter technique was applied to continuous waveforms from the regional network, substantially reducing the magnitude threshold for detection. Sequences of foreshocks preceding the two mainshocks are clearly seen, exhibiting different behaviors: a migration of the seismicity along the entire fault segment on the long-term and a concentration around the epicenters of the large events on the short-term. Suggesting that both seismic and aseismic slip during the foreshock sequences change the stress state on the fault, bringing it closer to failure. Furthermore, the observations also suggest that the MW4.7 event contributed to weaken the fault as part of the preparation process of the MW5.8 earthquake. Combining the results obtained from different settings, it becomes apparent that, regardless of the tectonic setting and degree of anthropogenic control over the seismicity, there is a wide range of complex nucleation behaviours not yet explained by any of the current models of earthquake nucleation. A simplistic view of earthquake nucleation as either a deterministic or a stochastic process seems inconsistent with the obtained results and fails to account for a more complex nucleation behaviour. Observations from The Geysers and the western Sea of Marmara earthquake sequence, suggest that both cascade triggering and aseismic slip can play major roles in the nucleation of moderate sized earthquakes. Both mechanisms seem to jointly contribute to fault initiation, even within the same rock volume. A separation of the two mechanisms can potentially be thought of at The Geysers, where cascade triggering seems to dominate in highly damaged parts of the reservoir, suggesting that the anthropogenic activity can at least partially influence the nucleation behavior of the occurring seismicity. This would be in agreement with the results obtained from analysis of hydraulic stimulations, where during the pressure-controlled phase of injection rupture growth is controlled by the injected fluid.

Description: Modern geodetic measurements have extraordinarily broadened our knowledge about plate tectonic kinematics by providing spatially and temporally dense crustal deformation constraints. Those measurements are particularily important for understanding tectonic processes at the Earth´s subduction zones that have been generating most devastating seismic events and tsunamis since the beginning of historical records. The hazard assessment of an active convergent margin mostly relies on geologic archive data as input for the earthquake recurrence concept that can be highly improved by robust kinematic models relating in-situ ground surface measurements to plate interface slip motion. In my thesis, I present an extensive analysis of crustal deformation variations during a subduction zone earthquake cycle in Northern Chile and hence contribute to the refinement of the subduction zone seismic cycle concept. I use GPS and InSAR measurements to constrain the purely tectonic signal and integrate a joint slip inversion model approach at the inter-, co- and postseismic stage of the mature Northern Chile-Southern Peru seismic gap. The characterization of crustal deformation is based on the case-study of the recent Mw 8.1 Iquique-Pisagua earthquake that ruptured the central part of the seismic gap on 1st April 2014. I compare interseismic ground motion rates of a dense continuous and survey-mode GPS network including a time-series of more than ten years with postseismic deformation rates two years after this megathrust event. Moreover, I generate an updated interseismic coupling map of the Northern Chilean subduction zone and present afterslip at different stages of the postseismic period. The joint inversion of InSAR data from two different satellites (Radarsat-2 and TerraSAR-X) and GPS measurements yields different coseismic slip models of the mainshock and separately of the largest aftershock two days later. The Iquique-Pisagua earthquake ruptured a highly coupled patch of the subduction zone interface (Camarones segment). Presented coseismic slip models range at the lower magnitudinal level of published models, are less compact in their geometry and stop at the Iquique Low coupling zone at 21° S. Afterslip is also limited southwards interpreted as impediment through a seismotectonic barrier at this latitudinal range. Postseismic deformation lasts for about two years before relocking rates are equal to interseismic ground motion velocity. Causal factors for the barrier that may behaves as seismotectonic segment limitation involve crustal (forearc) strength heterogeneities, interface coupling discontinuities potentially triggered by variations in seafloor roughness and differences in the subducting plate geometry. GPS observations south of the inferred seismotectonic barrier reveal a deformation rate increase in the second year after the earthquake. Afterslip models suggest a down-dip coupling increase as main driver for the rate increase, perhaps bringing the highly coupled southern Loa segment closer to failure. A megathrust event in Northern Chile was expected for more than thirty years based on slip deficit analysis and recurrence estimations. The fact that the Iquique-Pisagua earthquake 2014 did not rupture the entire Northern Chile- Southern Peru seismic gap like the last big event in 1877 (Mw 8.6 Iquique earthquake) is due to (1) tectonic pre-conditions that lowered the slip deficit as aseismic slow slip events and/or partial unlocking induced by seismic triggering of a foreshock sequence preceding the mainshock and (2) time-dependent, changing interface coupling conditions that may also change seismotectonic segment limitations over time. The Iquique-Pisagua event was not characteristic in the sense of the 1877 Mw 8.6 Iquique earthquake, but maybe for another smaller magnitudinal category of megathrust events that rupture more freuquently. The Northern Chile case-studie clearly demonstrates that subduction zone earthquakes are not only dependent on the slip deficit, but also on limitations of seismotectonic segments and tectonic pre-conditions as interface coupling variations. Thus, subduction zone earthquakes do not necessarily show same rupture characteristics over time. Taken together, the results of my thesis reveal (1) the interaction between different areas undergoing stress release and stress build-up in a major seismic gap, (2) constraints for the temporal variation of coupling degree and interface slip at different stages of the seismic cycle and (3) the influence of large earthquakes at adjacent segments at a subduction zone location and inferred implications for future seismic risk assessment.

Description: Moderne geodätische Messmethoden ermöglichen einen tiefen Einblick in räumlich und zeitlich hochauflösende krustale Deformationsprozesse und haben damit unser Wissen um kinematische Prozesse der Plattentektonik signifikant erweitert. Die Messmethoden sind vor allem wichtig, um tektonische Prozesse an den weltweiten Subduktionszonen zu studieren, an welchen seit Beginn historischer Aufzeichnungen die verheerendsten Erdbeben und Tsunamis entstehen. Die Gefährdungsanalyse eines aktiven, konvergenten Kontinentalrandes basiert zu großen Teilen auf geologischen Archivdaten als Basis des Konzepts für das periodische Wiederauftreten von Erdbeben, welches durch die robuste kinematische Inversion krustaler Deformation auf Bewegungen auf der Platten-Störungsfläche erheblich verbessert werden kann. In meiner Dissertation zeige ich umfangreiche Analysen krustaler Deformation und deren Variationen während eines kompletten Erdbebenzyklus in Nord-Chile und trage damit Wesentlich zur Verbesserung des Konzeptes des seismischen Subduktionszyklus bei. Ich nutze GPS und InSAR Messungen, um das tektonische Signal zu extrahieren und erstelle jeweils ein Inversionsmodell zur inter- co- und postseismischen Deformation in der tektonisch überfälligen nord-chilenischen-süd-peruanischen seismischen Lücke. Die Charakterisierung krustaler Deformation basiert auf der Fallstudie des aktuellen Mw 8.1 Iquique-Pisagua Erdbebens, welches den zentralen Teil der seismischen Lücke am 1. April 2014 brach. Ich vergleiche interseismische Bodenbewegungsraten eines dichten Netzwerkes aus kontinuierlichen und Kampagne- GPS Stationen von mehr als 10 Jahren mit postseismischen Deformationsraten von bis zu zwei Jahren nach dem Subduktionsbeben. Darüberhinaus generiere ich eine interseismische Plattenkopplungskarte der nord-chilenischen Subduktionszone und zeige Afterslip zu verschiedenen Zeiträumen der postseismischen Phase. Als Ergebnis der Inversion von InSAR-Daten zweier verschiedener Satelliten (Radarsat-2 und TerraSAR-X) mit GPS-Messungen präsentiere ich zwei verschiedene Slip-Modelle des Hauptbebens und separiert davon des größten Nachbebens zwei Tage später. Das Iquique-Pisagua Erdbeben brach einen hochgradig gekoppelten Bereich der Störungszone der subduzierenden Platte (im Camarones Segment). Meine co-seismischen Slip-Modelle sind eher am unteren Ende der Größenordnung bereits publizierter Modelle einzuordnen, zeigen eine weniger kompakte Geometrie und stoppten im Bereich eines sehr niedrig gekoppelten Plattenareals (Iquique-Low-coupling zone) bei 21° S. Afterslip ist nach Süden begrenzt, was als seismische Barriere in dieser geographischen Breite interpretiert wird. Die Phase postseismischer Deformation dauert etwa zwei Jahre an, bevor tektonische Bewegungsraten wieder mit den interseismischen Boden-Geschwindigkeiten vergleichbar sind. Die Entstehung einer solchen Barriere, welche möglicherweise als seismotektonische Segmentgrenze dient, geht zurück auf Festigkeitsunterschiede der Erdkruste, Kopplungs-Diskontinuitäten auf der Platten-Störungsfläche, verursacht durch Bathymetrieundulationen uund Geometrievariationen der subduzierenden Platte. GPS Messungen südlich der seismotektonischen Barriere zeigen einen Geschwindigkeitsanstieg innerhalb des zweiten Jahres nach dem Erdbeben. Afterslip-Modelle suggerieren, dass ein Anstieg der Plattenkopplung hauptverantwortlich ist für diesen Geschwindigkeitsanstieg, welcher das hochgekoppelte, südliche Loa Segment näher an einen Bruch der Platten-Störungszone bringt. Analysen eines Slip-Defizits und Abschätzungen des Erdbebenwiederkehrintervals ließen ein Subduktionsbeben in Nord-Chile seit mehr als 30 Jahren erwarten. Der Grund, dass das Iquique-Pisagua Erdbeben nicht die gesamte nordchilenische-südperuanische seismische Lücke gebrochen hat, wie es zuletzt 1877 beim Mw 8.6 Iquique-Beben geschehen ist, liegt in (1) den tektonischen Vorbedingungen und damit der Reduktion des Slip-Defizites durch ein aseismisches, langsames „stilles Erdbeben“ bzw. einer dem Hauptbeben vorangegangenen seismischen Vorschock-Sequenz, die eine partielle Platten-Entkopplung induzierte und (2) zeitlich variierende Konditionen der Kopplung an der Platten-Störungsfläche, die möglicherweise auch eine Verschiebung seismotektonischer Segmentgrenzen initiieren. Das Iquique-Pisagua Erdbeben war nicht charakteristisch in Bezug auf das Mw 8.6 Iquqiue Erdbeben von 1877, aber eventuell in Bezug auf eine andere Kategorie von kleineren Subduktionsbeben mit einer höheren Bruchfrequenz. Diese Fallstudie aus Nord-Chile beweist, dass Subduktionsbeben nicht ausschließlich abhängig vom Slip-Defizit sind, sondern auch von seismotektonischen Segmentgrenzen und tektonischen Vorbedingungen wie Kopplungsunterschieden. Daher zeigen Subduktionsbeben nicht unbedingt die selben Bruchcharakteristika über die Zeit. Zusammengefasst zeigen die Resultate meiner Dissertation (1) die Interaktion verschiedener Plattenareale, die Stressabbau und –aufbau in einer großen seismischen Lücke erfahren, (2) zeitliche Variation des Plattenkopplungsgrades und des Slips auf der Platten-Störungszone in verschiedenen Phasen des seismischen Zyklus und (3) den Einfluss eines großen Erdbebens auf benachbarte Segmente an einer Subduktionszone und daraus abgeleitete Implikationen zur seismische Gefährdungsanalyse.

Description: Cliffs line many erosional coastlines. Localized failures can cause land loss and hazard, and impact ecosystems and sediment routing. Links between cliff erosion and forcing mechanisms are poorly constrained, due to limitations of classic approaches. Combining multi-seasonal seismic and drone surveys, wave, precipitation and groundwater data we study drivers and triggers of seismically detected failures along the chalk cliffs on Germany's largest island, Rügen. The network consists of four (later five) seismic stations along the 8.6 km long chalk cliff coast. Waveforms are available from the Geofon data centre, under network code 4K, and are embargoed until Jan 2021.