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The Okitsu mélange in the Shimanto accretionary complex, the onshore extension of the modern Nankai accretionary prism, consists of a kilometer-size duplex of oceanic basalt and trench-fill sedimentary rocks, and is thought to represent rocks underplated to the prism along the subduction plate-boundary at seismogenic depth. An internal, horsebounding thrust of the duplex, referred to as the Suzume fault, juxtaposes basalt in the hanging wall and sedimentary rocks in the footwall. Structure and fabric of the fault was characterized at the mesoscale to investigate the processes and structural evolution along a plate-boundary décollement. The fault zone in the hanging wall consists of decimeterthick ultracataclasite bounded by a several m thick zone of fractured basalt, and likely records 2+ km displacement along the thrust. The footwall consists of decimeter-thick ultracataclasite bounded by a 20-m-thick zone of ductile shear in flattened sedimentary host rock, and likely records 30+ km of displacement. The asymmetric structure across the Suzume fault, as well as inferred displacement fields and timing relations, are consistent with a tectonic model in which the footwall records early ductile, compactive deformation of poorly consolidated sediments during underthrusting at the prism toe region, followed by extremely localized cataclasis at the underplating depth. In contrast, the hanging wall is deformed by intense cataclasis, and only during underplating. Deformation style and strain state in the footwall of the Suzume fault is qualitatively similar to the modern Costa Rica underthrust section at the toe region. Similarity in the structure and fabric of the hanging wall between the Suzume fault and modern décollement zones sampled through scientific drilling suggests that intense cataclasis under horizontal contraction likely is a common feature for the hanging wall of the décollement zone throughout the toe to underplating regions. Structures in the Suzume fault that are not in common with the modern décollements imply progressive consolidation during underthrusting from the toe to underplating depths may be responsible for the localization of shear in the footwall. At several kilometers depth, displacement along the plate boundary is likely accommodated within an extremely narrow zone as recorded in the ultracataclasite of the Suzume fault.

Störungszonen in den karbonatischen Wechselfolgen des Muschelkalks (Mittlere Trias) sind potenzielle Ziele für hydrothermale Projekte im Oberrheingraben (ORG). Es wurden verschiedene Methoden miteinander kombiniert, um die Permeabilitäts-Strukturen solcher Störungszonen, deren Spannungszustände und lokale Spannungsfelder abzuschätzen. Diese Arbeit kann damit zur Exploration von störungsgebundenen Muschelkalk-Reservoiren im ORG beitragen. Sie vergleicht diese mit einem bereits erfolgreich getesteten (störungsgebundenen) hydrothermalen Reservoir, den Sandsteinen des Buntsandsteins. Um für den Muschelkalk die Charakteristika von Störungszonen zu definieren und die zugehörige Permeabilitätsstruktur abzuschätzen, wurden verschiedene Störungszonentypen (z.B. Abschiebungen, invertierte Störungszonen, Schrägabschiebung) mit unterschiedlichen Maßstäben (Versatz: mittel-skalig 1-10 m, groß-skalig >10 m) detailliert untersucht. Eine Aufschlussanalogstudie zu einer groß-skaligen Störungszone (Schrägabschiebung) in dickbankigen Sandsteinen (Buntsandstein, Untere Trias) wurde zum Vergleich herangezogen. Der besondere Schwerpunkt lag jeweils auf der Charakterisierung von Bruchzone und Störungskern sowie des assoziierten Bruchsystems (Bruchdichte, Öffnungsweitenverteilung, Vernetzungsgrad, vertikale Ausdehnung). Die Daten zeigen, dass Bruchsysteme in eher homogenen Einheiten einen positiven Effekt auf die Reservoir-Permeabilität haben. Sie bieten, vor allem in der Nähe des Störungskerns, potenzielle Fließwege auch über mehrere Schichten und zeigen eine starke Vernetzung zwischen vergleichsweise kurzen Brüchen. Im Gegensatz dazu scheinen störungsgebundene Bruchsysteme in Einheiten mit einer starken mechanischen Schichtung einen geringeren Einfluss auf die Reservoirpermeabilität zu haben. Störungskerne zeigen stellenweise eine signifikante Komplexität, da sie vor allem abdichtende aber stellenweise auch durchlässige Strukturen aufweisen. Groß-skalige Störungszonen (im Reservoir-Maßstab) lassen sich für beide potenzielle Reservoirhorizonte am besten als kombinierte Barriere-Leiter-Systeme beschreiben. Diese Barriere-Leiter-Systeme zeichnen sich durch ein potenziell hydraulisch durchlässiges Bruchsystem in der Bruchzone (und im Buntsandstein zusätzlich in der Übergangszone) sowie einen schwach durchlässigen bis abdichtenden Störungskern aus. Um die Kenntnisse zum lokalen Spannungsfeld in Störungszonen im geschichteten Muschelkalk (Reservoirtiefe: 2.900 m) zu verbessern, wurden mit der Finite-Elemente-Software COMSOL Multiphysics® numerische 3D-Modelle erstellt. Es wurden deutliche Unterschiede des lokalen Spannungsfelds in Abhängigkeit von (1) der Orientierung, (2) dem Einfluss der maximalen Horizontalspannung SH im Spannungsregime, (3) Störungszonen-Maßstab und (4) den Kontrasten der mechanischen Eigenschaften festgestellt. In Spannungsregimen mit starker horizontaler Kompression wurde für Spannungsmagnituden und Versatz eine deutliche Abhängigkeit von der Orientierung der Störungszone festgestellt. Vor allem groß-skalige Störungszonen mit einem 30°-Winkel zu SH scheinen einen SH-induzierten Horizontalversatz innerhalb weicher Störungszoneneinheiten zu begünstigen; in dieser wurden die höchsten Versatzbeträge festgestellt. Die typische Abnahme von Spannungsmagnituden in weicheren Störungszoneneinheiten verringert sich in Richtung von Störungszonen, die senkrecht zu SH streichen. Der Einfluss der mechanischen Schichtung steigt mit zunehmender horizontaler Kompression, was zu einem vertikal heterogenen Spannungsfeld führt. Um Annahmen zu einer möglichen hydraulischen Aktivität einer Störungszone zu treffen, werden für die untersuchten Störungszonen analytische Abschätzungen zu Bewegungs- und Dehnungstendenzen unter Reservoir-Bedingungen präsentiert. Die Ergebnisse zeigen unterschiedliche Spannungszustände der analysierten Störungszonen, die auf das rezente Übergangsregime sowie unterschiedliche Orientierungen der maximalen Horizontalspannungen SH zurückzuführen sind. In dieser Arbeit präsentierte Ergebnisse von Aufschlussanalogstudien helfen dabei, fundierte Annahmen zur Permeabilitätsstruktur von Störungszonen zu treffen und damit vielversprechende Bohrziele im ORG zu definieren. In diesem Zusammenhang konnten sedimentäre Wechselfolgen identifiziert werden, die als potenzielle geothermische Reservoire ausgeschlossen werden können. Die Ergebnisse der numerischen 3D-Modellierungen können dazu beitragen, möglicherweise nötige Stimulationsmaßnahmen im Muschelkalk Reservoir optimal auszulegen. Darüber hinaus bieten die Ergebnisse die Möglichkeit, Einblick in potenzielle Probleme während der Bohrungsherstellung in Muschelkalk-Reservoiren zu bekommen, wie zum Beispiel die Wahrscheinlichkeit eines vertikal heterogenen Spannungsfeldes.

The North Anatolian Fault Zone (NAFZ) in Turkey is a major continental strike-slip fault, 1200 km long and with a current slip rate of 25 mm/yr. Historical records show that the NAFZ is capable of producing high-magnitude earthquakes, activating different segments of the fault in a westward progression. Currently, the NAFZ poses a major seismic hazard for the city of Istanbul, which is situated close to one of the two strands into which the fault splays in northwestern Turkey. Understanding of fault zone structure and properties at depth is essential to constrain where deformation occurs within the lithosphere and how strain localises with depth. In fact, geodynamic models explaining surface deformation require knowledge of the width and depth extent of the fault zone in both the crust and upper mantle. In this framework, this thesis aims to provide better constraints on fault zone geometry within the lithosphere. To achieve this objective P and S wave teleseismic tomography have been applied to the data recorded by a dense array of broadband seismic stations (DANA, Dense Array for Northern Anatolia); through teleseismic tomography it was possible to image the NAFZ structure in both the crust and uppermost mantle. In addition, joint inversion i of P-wave teleseismic data and local earthquake data collected using the same array provided a greatly improved resolution within the upper 20 km of the crust. Results from this work highlighted the presence of a shear zone associated to the northern branch of the NAFZ in the study area. The fault zone appears to be 15 km wide within the upper crust and narrows to < 10 km within the lower crust and to Moho depth. In the uppermost mantle its width is constrained to be 30 to 50 km.

Arcing eastward from the deep gorge of Cataract Canyon on the Colorado River is a series of aligned valleys (graben) and ridges (horst). This unusual landscape has formed as subsurface salt deforms toward the river and dissolves away, causing the overlying rocks to fault, slide, and subside. Geologists have long been interested in this actively evolving area they call the Needles fault zone, because understanding its mechanics and origin may shed light on how faults work in general and similar, yet inaccessible places like offshore rift zones or even the surface of the Moon. Despite this interest, the timing and long-term patterns of deformation here and are poorly constrained. This study uses analysis of digital landscape models to better delineate these patterns and provide better age constraints on the development of the Needles fault zone. We find that the Colorado River incision that led to deformation here began as recently as 1 million years ago, and that faulting due to subsurface salt movement initiated between 700 and 200 thousand years ago. The first part of this study takes advantage of how the development of graben valleys has changed the path of many of the streams in the study area, resulting in numerous captured streams terminating into a type of sinkhole, called a swallow hole, that develops above opening faults. These fissures are so named because, by ongoingopening, they are “swallowing” material that is flushed into them by local drainages. By recording and numerically dating the exposed upper 6-14 m of basin-fill strata, we determined that sediment was deposited to an alluvial fan and to ponded water. We also compared calculated sediment yields over time to paleoclimate records for the region to test extant hypotheses about how drylands respond to changing climate of the same scale as modern climate change. Against expectations, our results suggest that the greatest sediment yield and storage in these upper basins occurred during the relatively warm and dry time from 9 to 5 thousand years ago, when overland flow to transport sediment was weak. This implies that we are actually measuring sediment storage, as the faults that form swallow holes were relatively less active, allowing sediment to accumulate, rather than be flushed out of the basins.

The Copper Creek thrust fault in the southern Appalachians places Cambrian over Ordovician sedimentary strata. The fault accommodated displacement of 15-20 km at 100-180 °C. Along the hanging wall-footwall contact, microstructures within a ~2 cm thick calcite and shale shear zone suggest that calcite, not shale, controlled the rheology of the shear zone rocks. While shale deformed brittley, plasticity-induced fracturing in calcite resulted in ultrafine-grained (<1.0 μm) fault rocks that deformed by grain boundary sliding (GBS) accommodated primarily by diffusion creep, suggesting low flow stresses. Optical and electron microscopy of samples from a transect across the footwall shale into the shear zone, shows the evolution of rheology within the shear zone. Sedimentary laminations 1 cm below the shear zone are cut by minor faults, stylolites, and fault-parallel and perpendicular calcite veins. At vein intersections, calcite grain size is reduced (to ~0.3 μm), and microstructures include inter-and-intragranular fractures, four-grain junctions, and interpenetrating boundaries. Porosity rises to 6 percent from <1 percent in coarse (25 μm) areas of calcite veins. In coarse-grained calcite, trails of voids follow twin boundaries, and voids occur at twin-twin and twin-grain boundary intersections. At the shear zone-footwall contact, a 350 μm thick calcite band contains coarseand ultrafine-grained layers. Ultrafine-grained (~0.34 μm) layers contain microstructures similar to those at vein intersections in the footwall and display no lattice-preferred orientation (LPO). Coarse-grained layers cross-cut grain-boundary alignments in the ultrafine-grained layers; coarse grains display twins and a strong LPO. Within the shear zone, ultrafine-grained calcite-aggregate clasts and shale clasts (5-350 μm) lie within an ultrafine-grained calcite (<0.31 μm) and shale matrix. Ultrafinegrained calcite (<0.31 μm) forms an interconnected network around the matrix shale. Calcite vein microstructures suggest veins continued to form during deformation. Fractures at twin-twin and twin-grain boundary intersections suggest grain size reduction by plasticity-induced fracturing, resulting in <1 μm grains. Interpenetrating boundaries, four-grain junctions, and no LPO indicate the ultrafine-grained calcite deformed by viscous grain boundary sliding. The evolution of the ultrafine-grain shear zone rocks by a combination of plastic and brittle processes and the deformation of the interconnected network of ultrafine-grained calcite by viscous GBS enabled a large displacement along a narrow fault zone.

Geothermal research in the southern Canadian Cordillera has typically focused on hot spring systems and predicting maximum temperatures at depth, estimating fluid circulation depths, and investigating the distribution of hot spring systems and their relation to major geological features that often control thermal fluid flow. Detailed fieldwork to develop local and regional conceptual models of these systems has rarely been conducted and to our best knowledge, never in partnership with a First Nations. The scope of this project was to work collaboratively with the local First Nation to conduct detailed structural, hydrologic and hydrogeologic fieldwork to develop local and regional conceptual models of Sloquet Hot Springs, on unceded St'at'imc territory. To motivate our research and provide a successful example of geoscience research in the era of reconciliation and Indigenous resurgence, we review how resource regulation, research, reconciliation, and resurgence interact in British Columbia and detail our approach to community engagement. Detailed studies resulted in the development of a working conceptual model for the hydrogeothermal system at Sloquet Hot Springs. The conceptual model synthesizes local and regional groundwater flow, observed geothermal gradients, advective and conductive heat flow, as well as permeability contrasts in the subsurface to understand thermal fluid flow at the study site. Well monitoring, development, and pumping tests revealed numerous soft zones in the subsurface as well as bulk values for high transmissivity and hydraulic conductivity. Findings from subsurface investigations suggest bedrock in the area has significant permeability and that groundwater flow is controlled by steep hydraulic gradients caused by rugged topography in the region. The annual spring flux was calculated for Sloquet Hot Springs and used to approximate the recharge area that is required to drive the system. Although the study did not identify the primary fault that conveys high-temperature fluids, the potential locations of buried fault structures are hypothesized based on zones with observably high temperatures and flow along Sloquet Creek. / Graduate

This project examines the composition, structure, and geophysical properties of rocks sampled within the San Andreas Fault Observatory at Depth (SAFOD) borehole drilling experiment near Parkfield, California. Cuttings, sidewall cores, spot-core, and whole-rock core are examined from the meso- to micro-scale to characterize the nearfault environment at shallow crustal levels (0-4 km) along the central segment of the San Andreas fault. The central segment deforms by contiuous aseismic creep and microseismicity. An integrated approach utilizing core-logging, detailed structural core mapping, petrology, microstructural analyses, whole-rock geochemistry, borehole geophysics, and analog field studies is followed. At SAFOD, fractured granitic rocks and arkosic sediments are identified west of the San Andreas fault zone on the Pacific Plate; whereas sheared fine-grained sediments, ultrafine black fault-related rocks, and serpentinite-bearing fault gouge are present within and northeast of the fault zone on the North American Plate. Here, the fault consists of a broad zone of variably damaged rock containing localized zones of highly concentrated shear that often juxtapose distinct rock-types. Two zones of serpentinite-bearing clay gouge, each meters-thick are found in two locations where active aseismic creep was identified in the borehole. The gouge is composed of Mg-rich clays, serpentinite (lizardite ± chrysotile) with notable increases in magnetite, and Fe-, Ni-, and Cr-oxides/hydroxides and Fe-sulfides relative to the surrounding host rock. Organic carbon is locally high within fractures and bounding slip surfaces. The rocks adjacent to and within the two gouge zones display a range of deformation including intensely fractured regions, blockin- matrix fabrics, and foliated cataclasite structure. The blocks and clasts predominately consist of competent sandstone and siltstone embedded in a clay-rich matrix that displays a penetrative scaly fabric. Mineral alteration, veins, fracture-surface coatings, and slickelined surfaces are present throughout the core, and reflect a long history of syndeformation and fluid-rock reaction that contributes to the low-strength and creep in the meters-thick gouge zones. Evaluation of borehole geophysical data and elastic modulii for the lithologic and structural units identified in the SAFOD Phase 3 core reveal a correlation between composition and textures and the structural and/or permeability architecture of the SAF at SAFOD. Highly reduced velocity and elastic modulii surround the two serpentinitev bearing gouge zones, the Buzzard Canyon fault to the southwest, and another bounding fault to the northeast. Velocity and elastic moduli values on the Pacific Plate or southeast of the active fault trace intersected by SAFOD are much higher relative to the values measured on the North American Plate, or northeast of the fault trace. Within and adjacent to the two active gouge zones, the rock properties are highly variable over short distances, however, they are significantly lower relative to material outside of the fault zones. This research contributes critical evidence for rock properties and slip behavior within an active plate boundary fault. Results from this research and the SAFOD experiment help to constrain numerous hypotheses related to fault zone behavior and earthquake generation within central California.

The Eureka Lilly fault zone provides an impermeable barrier for groundwater flow in the East Tintic mining district. The fault zone separates two distinct groundwaters that have different temperatures, compositions, and potentiometric surfaces. The damage zone of the fault is an extensive network of interconnected open fractures and fault intersections that provide conduits for groundwater flow in otherwise impermeable units. The fault core breccia has been re-cemented and mineralized, which eliminates porosity in the rock by creating a thick impermeable zone, which has compartmentalized groundwaters across the fault zone. The compartmentalization of groundwater shows that fault zone variability (from strain partitioning and multiple deformation episodes) make traditional basin flow concepts inaccurate and difficult to apply in this area.

The structure and regional tectonic setting of an exhumed, 9.3-km long, left-lateral strike-slip fault zone eludicates processes of growth, linkage, and termination for strike-slip fault zones in granitic rocks. The Gemini fault zone is composed of three steeply dipping, southwest-striking, noncoplanar segments that nucleated and grew along preexisting joints. The fault zone has a maximum slip of 131 m and is an example of a segmented, hard-linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and host rock resulted in nonuniform slip orientations, complex interactions at fault segments, and an asymmetric slip-distance profile. Regional structural analysis shows that joints and left-lateral fault zones have accommodated slip within a 4.8-km wide, right-lateral monoclinical kink band with vertical fold axes and northwest-striking axial surfaces. Geometric modeling of the kink band indicates that as little as 1.1 km of right-lateral displacement across the kink band may have produced the observed slip on kilometer-scale faults within the kink band.