Dissertations / Theses on the topic 'Fault damage zones'

Quantification of the fluid flow properties of the Earth's crust is an essential precursor to the understanding of a wide range of geological processes, including earthquake generation and crustal strength, and the recovery of natural resources. Faults playa key role in the migration of fluids around the ;Earth's crust, and therefore the fluid flow properties of fractured rocks and how these properties evolve with time are of major importance. This thesis aims to improve our understanding of the hydraulic transport properties of large fault zones by presenting a large dataset of detailed field and microstructural observations and results from a suite of laboratory experiments to provide a basis for studying the distribution, and fluid flow properties, of damage surrounding large natural fault zones. Damage surrounding the core of faults is represented by both microfracturing of the rock matrix and by macroscopic fracture networks. Microfracture and macrofracture densities and orientations have been analysed on strike slip faults with displacements ranging over 3 orders of magnitude (~O.l2 m - 5000 m). These faults cut crystalline rock within the excellently exposed Atacama Fault Zone, Northern Chile. All faults consist of a fault core and associated damage zone. Damage zone width as defined by macrofractures and microfractures scale with displacement and fault length. Both microfractures (specifically fluid inclusion planes) and macrofractures within the damage zone show a log-linear .decrease in fracture density with perpendicular distance from the fault core. An empirical equation for microfracture density distribution based on the evolution of displacement has been derived for these faults. Preferred microfracture orientations in the damage zone suggest that this damage may predominantly be due to early processes related to enhanced stress at fault tips, in addition to cumulative wear processes from the juxtaposition of geometrical irregularities on the fault plane and damage from dynamic rupture. Fault core widths scale with displacement, with the largest displacement fault showing a wide multiple core zone. Detailed experimental studies of the development of permeability of crustal rock during deformation are essential in helping to understand fault mechanics and constrain larger scale models that predict bulk fluid flow within the crust. The strength, permeability and pore fluid volume evolution of initially intact crystalline rock under increasing differential load leading to macroscopic failure has been determined at water pore pressures of 50 MPa and varying effective pressures from 10 to 50 MPa. Permeability is seen to increase by, up to, and over two orders of magnitude prior to macroscopic failure, with the greatest increase seen at lowest effective pressures. Post-failure permeability is shown to be over three orders of magnitude higher than initial intact permeabilities and approaches the lower the limit of measurements of in situ bulk crustal permeabilities. Increasing amplitude cyclic loading tests show permeabilitystress hysteresis with high permeabilities maintained as differential stress is reduced and the greatest permeability increases are seen between 90-99% of the failure stress. Under hydrothermal conditions without further loading, it is suggested that much of this permeability can be recovered by healing and sealing, and pre-macroscopic failure fracture damage may heal relatively faster than post-failure macroscopic fractures. Pre-failure permeabilities are nearly seven to nine orders of magnitude lower than that predicted by some high pressure diffusive models suggesting that microfracture matrix flow cannot dominate, and agrees with inferences that bulk fluid flow and dilatancy must be dominated by larger scale structures, such as macrofractures. It is suggested that the permeability of a highly stressed fault tip process zone in low-permeability crystalline rocks could increase by more than 2 orders of magnitude, while stress drops related to fracture propagation close damage zone cracks, and some permeability is maintained due to hysteresis from permanent microfracture damage. Future work should aim to quantify experimentally-induced microfractures and. associated permeability measurements, and by relating the fracture densities surrounding natural fault zones with densities seen in experimental deformed samples with known permeabilities, modelling techniques can then be applied to gain estimates of bulk fluid flow of the fracture networks. This will provide a basis for predicting the influence of pore fluid pressures on important geological issues, such as crustal strength.

The demand for metals combined with diminishing near surface resources has prompted the increasing development of complex and unprecedented open pit designs to recover deeper resources. These designs include pushback extensions, intentional over-steepening of toes, or the transition to underground retreat or mass mining methods. While past designs rarely involved pit depths exceeding 500 m, steeper and deeper designs approaching or exceeding 1000 m are now considered. Experiences with large open pits demonstrate that complex failure mechanisms occur with higher propensity within these slopes. New technologies used to monitor slope displacement, such as radar interferometry, along with increased real-time data processing have given engineers more data and faster tools to investigate the fundamental rock mechanics that occur within large slopes. Radar allows for the collection of large amounts of real-time data with millimeter precision. Emphasis is given in this thesis to the use of radar monitoring in resolving displacements in proximity to fault damage zones. Research was conducted to develop and execute a first of its kind 3-D radar experiment involving the simultaneous deployment of two radar systems. This experiment demonstrates that valuable knowledge, in the form of a 3-D displacement map, was used to resolve the influence of large fault zones in promoting complex slope deformation kinematics and failure mechanisms. In parallel, numerical modelling continues to develop as a key tool in understanding deep-seated rock slope deformation mechanisms. Research was conducted to investigate the characterization and representation of key fault properties within sensitivity analyses used to provide guidance on the impact of simplification of these complex structures. Representative geometries and input parameters based on case studies were used to show the influence of fault location, orientation and complexity, on stress heterogeneity created by the interaction between faults and deepening large open pits, as well as the transition to underground mass mining. These interactions can create zones of plastic shear strain or extensional strain damage not typically accounted for in most stability analyses. The inclusion of stress heterogeneity and subsequent rock mass damage is shown to modify the observed mechanisms of slope movement and allow previously unviable kinematics to develop.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Les séismes le long de grandes failles crustales représentent un danger énorme pour de nombreuses populations. Le mécanique de ces failles est influencé par des zones endommagées qui entourent le coeur de faille. La fracturation dans ces zones contrôle chaque étape du cycle sismique. En effet, cette zone contrôle la mécanique de la rupture sismique, elle est un conduit pour les fluides, réagit chimiquement sous l'effet de fluides réactifs, et facilite la déformation pendant les périodes post- et inter-sismiques. Dans cette thèse de doctorat, des expériences de laboratoire ont été réalisées pour mieux comprendre 1) la façon dont l'endommagement est généré pendant le chargement transitoire co-sismique, 2) comment l'endommagement permet de mieux contraindre le chargement co-sismique le long de grandes failles, et iii) comment les fractures peuvent se cicatriser au fil du temps et contrôler l'évolution de la perméabilité et de la résistance mécanique de la faille.L'introduction de la thèse propose une revue critique de la littérature sur la génération de dommages co-sismiques et en particulier sur la formation des roches pulvérisées. Le potentiel de ces roches comme marqueur des déformations co-sismiques est discuté. Bien que ces roches pulvérisées soient prometteuses pour ces aspects, plusieurs questions restent ouvertes.L'une de ces questions concerne les conditions de chargement transitoire nécessaires pour atteindre la pulvérisation. Le seuil de taux de deformation pour atteindre la pulvérisation peut être réduit par des endommagemments progressifs, au cours de ruptures sismiques successives. Des barres de Hopkinson ont été utilisées pour effectuer des chargements dynamique successifs d'une roche cristalline (monzonite). Les résultats montrent que le seuil pour atteindre la pulvérisation est réduit d'au moins 50% lorsque des chargements successives sont imposés. Cette thèse discute aussi pourquoi les roches pulvérisées sont presque toujours observées dans des roches cristallines et peu dans des roches sédimentaires poreuses. Pour comprendre cette observation, des expériences à haute vitesse de déformation ont été effectuées sur des grès de Rothbach. Les résultats montrent que la pulvérisation des grains eux mêmes ne se produit pas dans les grès. L'endommagement reste se produit principalement à une échelle supérieure à celle grains, et des bandes de compaction sont observées. La compétition entre l'endommagement inter- et intra-granulaire est expliquée par les paramètres microstructuraux en combinant deux modèles micromécaniques classiques. Les microstructures observées dans les grès peuvent se former dans le régime quasi-statiques et aussi dans le régime dynamique. Par conséquent, il est recommandée d'être prudent lors de l'interprétation du mécanisme de deformation dans les roches sédimentaires proches de la surface. La dernière question abordée durant la thèse est la cicatrisation post-sismique de fractures co-sismiques. Des expériences ont été réalisées pour cicatriser des fissures par précipitation de calcite. Le but est l'étude du couplage entre l'augmentation de résistance mécanique de la roche fissurée et l'évolution de la perméabilité. Les échantillons fracturées ont été soumis à des conditions de pression et températures similaires de la croûte supérieure et à une percolation d'un fluide sursaturé en calcite pendant plusieurs mois. Ce couplage non-existe dans les premières étapes de la cicatrisation. Il est révélé par l'imagerie par tomographie aux rayons X que le scellement naissant des fractures se produit dans les porosités situées en aval de barrières d'écoulement, et donc dans des régions qui ne touchent pas les principales voies d'écoulement du fluide. Le découplage entre l'augmentation de résistance de la roche et la perméabilité suggère que les zones d'endommagement peu profondes dans les failles actives peuvent rester des conduits actifs pour les fluides plusieurs années après un séisme
Earthquakes along large crustal scale faults are a huge hazard threatening large populations. The behavior of such faults is influenced by the fault damage zone that surrounds the fault core. Fracture damage in such fault damage zones influences each stage of the seismic cycle. The damage zone influences rupture mechanics, behaves as a fluid conduit to release pressurized fluids at depth or to give access to reactive fluids to alter the fault core, and facilitates strain during post- and interseismic periods. Also, it acts as an energy sink for earthquake energy. Here, laboratory experiments were performed to come to a better understanding of how this fracture damage is formed during coseismic transient loading, what this fracture damage can tell us about the earthquake rupture conditions along large faults, and how fracture damage is annihilated over time.First, coseismic damage generation, and specifically the formation of pulverized fault damage zone rock, is reviewed. The potential of these pulverized rocks as a coseismic marker for rupture mechanisms is discussed. Although these rocks are promising in that aspect, several open questions remain.One of these open questions is if the transient loading conditions needed for pulverization can be reduced by progressively damaging during many seismic events. The successive high strain rate loadings performed on quartz monzonites using a split Hopkinson pressure bar reveal that indeed the pulverization strain rate threshold is reduced by at least 50%.Another open question is why pulverized rocks are almost always observed in crystalline lithologies and not in more porous rock, even when crystalline and porous rocks are juxtaposed by a fault. To study this observation, high strain rate experiments were performed on porous Rothbach sandstone. The results show that pervasive pulverization below the grain scale, such as observed in crystalline rock, does not occur in the sandstone samples for the explored strain rate range (60-150 s-1). Damage is mainly occurs at a scale superior to that of the scale of the grains, with intragranular deformation occurring only in weaker regions where compaction bands are formed. The competition between inter- and intragranular damage during dynamic loading is explained with the geometric parameters of the rock in combination with two classic micromechanical models: the Hertzian contact model and the pore-emanated crack model. In conclusion, the observed microstructures can form in both quasi-static and dynamic loading regimes. Therefore caution is advised when interpreting the mechanism responsible for near-fault damage in sedimentary rock near the surface. Moreover, the results suggest that different responses of different lithologies to transient loading are responsible for sub-surface damage zone asymmetry.Finally, post-seismic annihilation of coseismic damage by calcite assisted fracture sealing has been studied in experiments, so that the coupling between strengthening and permeability of the fracture network could be studied. A sample-scale fracture network was introduced in quartz monzonite samples, followed exposure to upper crustal conditions and percolation of a fluid saturated with calcite for several months. A large recovery of up to 50% of the initial P-wave velocity drop has been observed after the sealing experiment. In contrast, the permeability remained more or less constant for the duration of the experiment. This lack of coupling between strengthening and permeability in the first stages of sealing is explained by X-ray computed micro tomography. Incipient sealing in the fracture spaces occurs downstream of flow barriers, thus in regions that do not affect the main fluid flow pathways. The decoupling of strength recovery and permeability suggests that shallow fault damage zones can remain fluid conduits for years after a seismic event, leading to significant transformations of the core and the damage zone of faults with time

This study area provides a unique opportunity to study the intersection of the Elsinore and West Salton detachment faults in southern California, effusing warm springs, and alteration products in the midst of the fault intersection. Structural mapping and compiling previous maps supply an interpretation of the fault zone geometries within the Tierra Blanca Mountains. Geochemical analysis of the crystalline basement and altered protolith help determine the effects of faulting and fluid flow in the study area. In the Tierra Blanca Mountains, the Elsinore strike-slip fault system transitions from the double-stranded Julian segment and Earthquake Valley fault in the northwest, to the single-stranded Coyote Mountain segment in the southeast. A network of cross faults striking northeast connects the fault segments. The Coyote Mountain segment encounters the inactive West Salton detachment fault in the study area. The detachment fault is a barrier to fluid flow and exhibits primarily brittle deformation, while the Coyote Mountain segment is a conduit for fluid flow along the northeastern flank of the Tierra Blanca Mountains. The damage zone of the Coyote Mountain segment reaches widths up to 500 m and contains intense fracturing and subsidiary faults striking parallel to the main trace. The tonalite protolith is bleached, stained, and altered from water-rock interactions. The most intense bleaching is at a county park, where the protolith is altered to clays and zeolites while the mineralogy of the stained regions contains iron oxides and clinochlore in addition to quartz, Ca-rich albite, and biotite preserved from the protolith. The water chemistry at Agua Caliente hot springs shows the fluid is partially equilibrated. Groundwater temperatures likely reached 75-85°C at depths up to 2.14 km before rising to the surface. Frequent seismicity in the study region is related to the spring characteristics including water level, conductivity, and temperatures. Spring temperature and conductivity displayed three behaviors during the summer 2011 logging period, attributed to seasonal changes and most likely local seismicity as well. Conductivity seems to be the property most influenced by earthquake activity in the area. Changes in fluid chemistry between sampling periods may indicate mixture with other fluid sources.

Carbonate reservoirs contain approximately two-thirds of the world's oil and gas reserves (Al-Anzi et al., 2003). Carbonates often pose a significant problem when it comes to understanding their reservoir quality because of their heterogeneous nature, which is caused by both the variety of processes occurring depositionally and their high susceptibility to diagenetic alterations. In order to fully characterise the behaviour of carbonate rocks in the subsurface is it important to understand their textural heterogeneity and also how faulting can modify their textures. Deformation in fault zones causes the petrophysical properties (e.g. porosity, permeability and velocity) to alter from the background values. For example, fracturing in damage zones surrounding faults increase the permeability, creating conduits to fluids, conversely, fault cores often act as barriers, created by pore occluding processes. However, faulting in carbonate rocks is often complicated by their textural variations, leading to a variety of deformation microstructures, and each will create different petrophysical properties. This thesis aims to understand how faulting effects different carbonate rocks and analyse the controls on any alterations to the petrophysical properties (porosity, permeability and velocity) into the fault zones. Alterations to the permeability are important to unravel in order to assess the fluid flow potential and hydraulic properties of a rock. Understanding the alterations to the velocity can help to better image faults at depth and to provide information on their microstructures.

My dissertation focuses primarily on the following three aspects associated with passing seismic waves in the field of earthquake seismology: temporal changes of fault zone properties, nonlinear site response, and dynamic triggering. Quantifying the temporal changes of material properties within and around active fault zones (FZ) is important for better understanding of rock rheology and estimating the strong ground motion that can be generated by large earthquakes. As high-amplitude seismic waves propagate through damaged FZ rocks and/or shallow surface layers, they may produce additional damage leading to nonlinear wave propagation effects and temporal changes of material properties (e.g., seismic velocity, attenuation). Previous studies have found several types of temporal changes in material properties with time scales of tens of seconds to several years. Here I systematically analyze temporal changes of fault zone (FZ) site response along the Karadere-Düzce branch of the North Anatolian fault that ruptured during the 1999 İzmit and Düzce earthquake sequences. The coseismic changes are on the order of 20-40%, and are followed by a logarithmic recovery over an apparent time scale of ~1 day. These results provide a bridge between the large-amplitude near-instantaneous changes and the lower-amplitude longer-duration variations observed in previous studies. The temporal changes measured from this high-resolution spectral ratio analysis also provide a refinement for the beginning of the longer more gradual process typically observed by analyzing repeating earthquakes. An improved knowledge on nonlinear site response is critical for better understanding strong ground motions and predicting shaking induced damages. I use the same sliding-window spectral ratio technique to analyze temporal changes in site response associated with the strong ground motion of the Mw6.6 2004 Mid-Niigata earthquake sequence recorded by the borehole stations in Japanese Digital Strong-Motion Seismograph Network (KiK-Net). The coseismic peak frequency drop, peak spectral ratio drop, and the postseismic recovery time roughly scale with the input ground motions when the peak ground velocity (PGV) is larger than ~5 cm/s, or the peak ground acceleration (PGA) is larger than ~100 Gal. The results suggest that at a given site the input ground motion plays an important role in controlling both the coseismic change and postseismic recovery in site response. In a follow-up study, I apply the same sliding-window spectral ratio technique to surface and borehole strong motion records at 6 KiK-Net sites, and stack results associated with different earthquakes that produce similar PGAs. In some cases I observe a weak coseismic drop in the peak frequency when the PGA is as small as ~20-30 Gal, and near instantaneous recovery after the passage of the direct S waves. The percentage of drop in the peak frequency starts to increase with increasing PGA values. A coseismic drop in the peak spectral ratio is also observed at 2 sites. When the PGA is larger than ~60 Gal to more than 100 Gal, considerably stronger coseismic drops of the peak frequencies are observed, followed by a logarithmic recovery with time. The observed weak reductions of peak frequencies with near instantaneous recovery likely reflect nonlinear response with essentially fixed level of damage, while the larger drops followed by logarithmic recovery reflect the generation (and then recovery) of additional rock damage. The results indicate clearly that nonlinear site response may occur during medium-size earthquakes, and that the PGA threshold for in situ nonlinear site response is lower than the previously thought value of ~100-200 Gal. The recent Mw9.0 off the Pacific coast of Tohoku earthquake and its aftershocks generated widespread strong shakings as large as ~3000 Gal along the east coast of Japan. I systematically analyze temporal changes of material properties and nonlinear site response in the shallow crust associated with the Tohoku main shock, using seismic data recorded by the Japanese Strong Motion Network KIK-Net. I compute the spectral ratios of windowed records from a pair of surface and borehole stations, and then use the sliding-window spectral ratios to track the temporal changes in the site response of various sites at different levels of PGA The preliminary results show clear drop of resonant frequency of up to 70% during the Tohoku main shock at 6 sites with PGA from 600 to 1300 Gal. In the site MYGH04 where two distinct groups of strong ground motions were recorded, the resonant frequency briefly recovers in between, and then followed by an apparent logarithmic recovery. I investigate the percentage drop of peak frequency and peak spectral ratio during the Tohoku main shock at different PGA levels, and find that at most sites they are correlated. The third part of my thesis mostly focuses on how seismic waves trigger additional earthquakes at long-range distance, also known as dynamic triggering. Previous studies have shown that dynamic triggering in intraplate regions is typically not as common as at plate-boundary regions. Here I perform a comprehensive analysis of dynamic triggering around the Babaoshan and Huangzhuang-Gaoliying faults southwest of Beijing, China. The triggered earthquakes are identified as impulsive seismic arrivals with clear P- and S-waves in 5 Hz high-pass-filtered three-component velocity seismograms during the passage of large amplitude body and surface waves of large teleseismic earthquakes. I find that this region was repeatedly triggered by at least four earthquakes in East Asia, including the 2001 Mw7.8 Kunlun, 2003 Mw8.3 Tokachi-oki, 2004 Mw9.2 Sumatra, and 2008 Mw7.9 Wenchuan earthquakes. In most instances, the microearthquakes coincide with the first few cycles of the Love waves, and more are triggered during the large-amplitude Rayleigh waves. Such an instantaneous triggering by both the Love and Rayleigh waves is similar to recent observations of remotely triggered 'non-volcanic' tremor along major plate-boundary faults, and can be explained by a simple Coulomb failure criterion. Five earthquakes triggered by the Kunlun and Tokachi-oki earthquakes were recorded by multiple stations and could be located. These events occurred at shallow depth (< 5 km) above the background seismicity near the boundary between NW-striking Babaoshan and Huangzhuang-Gaoliying faults and the Fangshan Pluton. These results suggest that triggered earthquakes in this region likely occur near the transition between the velocity strengthening and weakening zones in the top few kms of the crust, and are likely driven by relatively large dynamic stresses on the order of few tens of KPa.

The Chelungpu thrust fault, Taiwan, and the Mozumi right-lateral fault, Japan, provide an opportunity to characterize active faults in clastic sedimentary rocks and provide constraints to seismologic models. The northern Chelungpu fault has a 10-30 m wide primary damage zone characterized by dense fractures and chemical alteration. The southern Chelungpu fault has a 25-70 m wide primary damage zone characterized by dense fractures, alteration, intensely sheared rock, and secondary faults. The complexity of the damage zone, geochemistry, and clay mineralogy of the southern fault zone reflects its greater maturity (~1 Ma) relative to the northern fault zone (~46-100 Ka). A transition exists from smectite in exhumed fault core to illite-rich fault core at depth (200 - 1000 m) due to co-seismic fluid flow and radiated seismic energy. Clay composition plays a role in fault weakening. Microstructures in deformed Mozumi siltstone indicate syn-tectonic fluid pressurization and flow, and shear concentrated in sericite-rich matrix. Kaolinite and illite clays dominate the host rock and fault breccia; illite, smectite, and kaolinite dominate clay-rich fault breccia. Whole-rock geochemistry shows a depletion of most oxides in fault rocks relative to unaltered host rock (up to ~90%). Resistivity values are depressed by 0-50 ohm-m, and νp and νs are decreased by ~0.30 km/s and ~0.40 km/s across the main fault relative to wall rock, and an average of ~0.70 km/s and ~1.0 km/s relative to host rock, respectively. Calculated values of Young’s modulus and Poisson’s ratio of fault rocks range from 16.2 to 44.9 GPa and 0.263 to 0.393, respectively. The protolith has a calculated Young’s modulus of 55.4 GPa and a Poisson’s ratio of 0.242. Lowest values of Young’s modulus and highest values of Poisson’s ratio correspond to fault breccia with high fluid content, and are offset from the most altered and damaged fault rocks. Fluid-rich pockets, and thus alteration, apparently migrate through the fault zone and may facilitate creep on the Mozumi fault because these fluid rich rocks are unable to sustain the shear stresses needed for brittle failure. The Chelungpu and Mozumi faults illustrate the temporally dynamic and heterogeneous nature of active fault zones.

L’étude des failles affectant la croûte supérieure suscite un intérêt particulier pour la modélisation de leur impact sur l’écoulement des fluides et le comportement mécanique de la croûte terrestre. Les zones d’endommagements de failles sont d’importantes structures aux multiples implications pour les problématiques de gestions des ressources et de risque/aléa sismiques. Cette thèse a pour objectif de déterminer la distribution de l’endommagement autour des failles, comprendre sa croissance et étudier son impact sur la loi d’échelle Déplacement – Epaisseur d’endommagement (D-T). Pour répondre à cette problématique, deux approches complémentaires sont développées : des études tectoniques d’exemples naturels et des modélisations analogiques de failles normales. Ce manuscrit présente de nouvelles cartographies de l’endommagement, une première loi D-T pour les failles dans des roches carbonatées, ainsi que les premières expériences de modélisation analogique dédiées à l’étude de l’endommagement. Les résultats montrent que la distribution de l’endommagement autour des failles est hétérogène et asymétrique, principalement influencée par les nombreuses interactions de failles lors de leur croissance (segmentation, failles conjuguées). Une loi D-T spécifique à l’endommagement de type wall damage est établie, qui montre une corrélation normale entre D et T pour les failles de rejet inférieur à 100 m et confirme l’existence d’un seuil d’épaisseur d’endommagement au-delà de 100 m de rejet. Pour expliquer cette loi nous proposons un modèle de croissance de zone d’endommagement contrôlée par les processus d’interaction et de coalescence de la segmentation précoce. Les expériences de modélisations analogiques ont permis de décrire deux nouveaux types d’endommagement (graben damage et dip-change link damage), et d’identifier une transition de mode de déformation, depuis un cisaillement dilatant segmenté vers un cisaillement compactant localisé dans les zones de failles. Elles démontrent également que l’initiation de la segmentation, la sélection de l’activité des segments, leurs interactions et leurs coalescences sont des processus essentiels contrôlant le développement des zones d’endommagement et la loi D-T. Nous proposons que l’épaisseur de l’unité fragile contenant les failles est un paramètre principal du contrôle de l’évolution de la segmentation, de la localisation de la déformation et donc du seuil d’épaisseur d’endommagement observé
The study of faults in the upper crust generates interest in modeling their impact on fluid flow and the mechanical behavior of the earth's crust. Fault damage zones are important structures with multiple implications for resource management and earthquake studies. This thesis aims to characterize the distribution and growth of damage around faults and to study its impact on the Displacement - Damage thickness (D-T) scaling law. Two complementary approaches of field measurements and analog modeling of normal faults are developed to answer this question. This manuscript presents new results of fault damage mapping, D-T scaling in carbonate rocks, and the first analog modeling experiments of fault damage zones. The results show a heterogeneous and asymmetric distribution of damage around faults, mainly influenced by fault interactions during their growth (segmentation, conjugate faults). A D-T law specific to wall damage is established and shows a normal correlation between D and T for less than 100 m of fault displacement, and also confirms the existence of a damage thickness threshold after 100 m of displacement. To explain this law, we propose a damage zone growth model controlled by the interaction and coalescence of fault segments. Analog modeling experiments allowed the description of two new types of damage (graben damage and dip-change link damage), and show a failure mode transition during fault growth, from a segmented dilatational-shear mode to a localized compactional-shear mode. They also demonstrate that initiation of segmentation, segment activity selection, interaction and coalescence processes control the development of fault damage zones and the D-T law. We propose that the thickness of the faulted brittle layer is a main controlling parameter of segmentation, strain localization, and the fault damage thickness threshold observed

Les zones de failles concentrent la migration de fluides et la déformation dans la croûte supérieure. Les propriétés hydrauliques des formations argileuses en font des excellents sites de stockage et des roches mères performants. Les zones de failles peuvent jouer deux rôles contraires dans la circulation de fluides, soit elles s’expriment sous forme de drains, soit elles constituent une barrière, et souvent les deux rôles sont combinés au sein d’une même zone de failles. Les processus de migration des fluides dans les zones de failles affectant les argiles sont peu connus. Cette étude s’est focalisée sur la structure, les paléo-circulations, les circulations actuelles lors de tests d’injection et les propriétés pétro-physiques de la zone de failles présente dans le laboratoire de recherche souterrain de Tournemire dans les argilites Toarciennes. La structure de la zone de failles a été caractérisée par des forages et reconstituée en 3D par modélisation numérique, permettant de définir des faciès de déformation. L’architecture de la zone de failles se caractérise par une imbrication de facies de déformations plus ou moins intenses sans claire organisation en cœur et zone endommagée comme observée dans les roches plus dures. Les zones intactes, fracturées et les brèches sont respectivement caractérisées par des porosités matricielles comprises entre 9.5-13.5, 10-15 et 13-21%. La circulation de fluide se concentrant aux limites de la brèche et au niveau des zones de failles «immatures» ou secondaires comprises dans les zones fracturées. Lors de son activité, la zone de failles a déjà été affectée par au moins deux phases de circulations de fluides
Fault zones concentrate fluids migration and deformations in the upper crust. The shale hydraulic properties make them excellent storage sites and hydrocarbon reservoirs/source rocks. Fault zones can play two roles in the fluid circulation; drains or barriers, in general, both roles are combined within the same fault zone. What are the conditions that promote the fluid circulation along the fault zones in shales and what are the fault zone impacts on the formation properties are relatively poorly explored key questions. This study focused on characterizing the relationships between fault architecture, paleo-fluid as well as current fluid circulations through the analysis of fault calcite mineralization, injection tests and petrophysical properties conducted on a fault zone outcropping underground in the Tournemire research laboratory nested in the Toarcian shale. The fault zone structure was characterized using boreholes data and reconstructed in 3D through modeling to define different deformation facies. No clear facies organization is observed, a fault core and a fault damage zone being difficult to define as it is in hard rocks. The intact, fractured and breccia facies are characterized by a porosity of 9.5-13.5, 10-15 and 13-21%. Large fluid flowrate concentrated along a few “channels” located at the breccia boundaries and in the secondary fault zones that displayed fractured facies and limited breccia fillings. Detailed microstructural and geochemical analysis at the breccia/fractured zones interface revealed that fluids circulated out of the main shear zones, in micro-more or less inherited fractures highlighting a decoupling between fault slip and fluid migrations

Spring water inflow is distinct at Pah Tempe Hot Springs (also known as Dixie Hot Springs) situated within the damage zone of the Hurricane Fault in Timpoweap Canyon in Hurricane, Utah. Excising of the footwall by the Virgin River has created Timpoweap Canyon and allowed an unusual opportunity to study the spring inflow in relation to the fault damage zone. While correlation of these springs with the damage zone and visible fracture patterns on the canyon wall has been made, no subsurface faulting has been imaged to verify connection to these visible fractures and spring inflows (Nelson et al., 2009). The stream was logged and contoured to note the varying locations of spring water inflows in contrast with unsaturated Virgin River water. Seismic surveys were conducted and subsurface profiles made to locate offsets and faults. Photogrammetry was conducted and a three-dimensional model of the canyon and cliff wall was created to facilitate remote fracture mapping of this wallSubsurface features correlate to fractures, spring water inflow locations, and surface faults mapped by Biek (2002). This suggests that faulting and fracturing from the Hurricane Fault provides subsurface conduits for these thermal waters to rise. In one area in the stream, thermal inflow correlates with both subsurface offsets and major surface fractures. Numerous correlations between just spring water entry and subsurface offsets or surface fractures are also found. Fracture and fault density is atypical at Pah Tempe as these features do not diminish with distance from the main strand of the fault. This has led to the Sevier Orogeny accounting for creating the observed fracture conduits at Pah Tempe. Fractures in the canyon wall at Pah Tempe open west to east. This is indicative of the maximum horizontal compressive stress of southern Utah being north to south (Zoback and Zoback, 2015). Therefore the spring inflow at Pah Tempe is likely a result of the damage from the Hurricane Fault creating conduits for spring water to rise, rather than the Sevier Orogeny.

Seismogenically active faults (those that produce earthquakes) are very complex systems that constantly change through time. When an earthquake occurs, the rocks surrounding a fault (the “fault rocks”) become altered or damaged. Studying these fault rocks directly can inform what processes operated in the fault and how the fault evolved in space and time. Examining these key aspects of faults helps us understand the earthquake hazards of active fault systems. The Mecca Hills, southern California, consist of a set of hills adjacent to the southernmost San Andreas Fault. The topography is related to motion on the San Andreas fault, which poses the largest seismic hazard in the lower forty-eight United States. The southernmost San Andreas fault, and the Mecca Hills study location may be reaching the end of its earthquake cycle and is due for a major, potentially catastrophic earthquake. The seismic hazards of the region, coupled with its proximity to major populated areas (Coachella Valley, Los Angeles Basin) make it a critical research area to understand fault zone evolution and the protracted history of fault development. The goal of this thesis was to directly examine the fault rocks in the Mecca Hills to understand how San Andreas-related faults in this area have evolved and behaved through time. This study integrates a variety of field and laboratory techniques to characterize the structural, geochemical, and thermal properties of the Mecca Hills fault rocks. The results herein document two distinct phases of deformation in the rocks exposed in the Mecca Hills, one around 24 million years ago and the other in the last one million years. This more recent phase of deformation is characterized by fault block exhumation and fluid flow in the fault zones, likely related to changing dynamics of the southernmost San Andreas Fault system. The older event informs how and when these rocks came close to Earth’s surface before the San Andreas Fault initiated.

A detailed structural study of Rock Canyon (near Provo, Utah) provides insight into Wasatch Range tectonics and fold-thrust belt kinematics. Excellent exposures along the E-W trending canyon allow the use of digital photography in conjunction with traditional field methods for a thorough analysis of Rock Canyon's structural features. Detailed photomontages and geometric and kinematic analyses of some structural features help to pinpoint deformation mechanisms active during the canyon's tectonic history. Large-scale images and these structural data are synthesized in a balanced cross section, which is used to reconstruct the structural evolution of this portion of the range. Projection of surficial features into the subsurface produces geometrical relationships that correlate well with a fault-bend fold model involving one or more subsurface imbrications. Kinematic data (e.g. slickenlines, fractures, fold axes) indicate that the maximum stress direction during formation of the fault-bend fold trended at approximately 120°. Following initial thrusting, uplift and development of a thrust splay produced by duplexing may have caused a shift in local stresses in the forelimb of the Rock Canyon anticline leading to late-stage normal faulting during Sevier compression. These normal faults may have activated deformed zones previously caused by Sevier folding, and reactivated early-stage decollements found in the folded weak shale units and shaly limestones. Movement on most of these normal faults roughly parallels stress directions found during initial thrusting indicating that these extensional features may be coeval with thrusting. Other zones of extension and brittle failure produced by lower ramp geometry appear to have been activated during Tertiary Basin and Range extension along the Wasatch Fault Zone. Slickenline data on these later normal faults suggest a transport direction of nearly E-W distinguishing it from earlier events.

It is widely recognised that inverted fault zones form economically significant structures for subsurface fluid exploration and production. Inverted fault zones are formed by the contractional reactivation and reversal of pre-existing extensional fault zones. Recognising the reverse-reactivation of normal faults in sedimentary basins is fundamental, as the reconfiguration of fault geometries has implications for overall basin geometry, sediment accommodation and supply, and fluid flow pathways. This is particularly important for understanding the modification or creation of petroleum system elements through time, which in turn allows for increased targeted exploration. Notwithstanding the broad economic relevance of inverted fault zones, integrated multi-scale (from micrometre-scale to outcrop-scale) studies on the structural, petrophysical, and geochemical properties of inverted fault zones within porous reservoir rocks are limited. This thesis characterises the structural, petrophysical, and geochemical properties of inverted fault zones from two localities, the Otway Basin (Australia) and Bristol Channel Basin (United Kingdom), in order to understand how inverted faults influence fluid flow at a range of scales. To address this, this thesis has two main topics of focus: (1) identify the influence of inverted faults on surrounding lithology by assessing the relationship between faults, damage zones around faults, and fractures related to fault growth; and (2) identify how subsurface fluids flow, interact, and modify their surrounds by assessing the geochemistry of fluids in fractures and thereby constraining the source, evolution, and migration of fluids preserved in fractures. An integrated, multi-scale approach is crucial for improving the prediction of subsurface fluid flow beyond the wellbore. In order to understand the influence of inverted faults on surrounding lithology, an inverted fault (Castle Cove Fault) in the Otway Basin, southeast Australia, is the focus of the first two chapters of this thesis. The geometries and relative chronologies of natural fractures adjacent to the Castle Cove Fault are investigated. Structural mapping in the hanging wall damage zone reveals three sets of shear fractures that are geometrically related to the Castle Cove Fault. Inversion of the Castle Cove Fault has resulted in the development of an extensive network of fractures and complex fold structures, and inversion would have subsequently improved the outcrop-scale permeability structure of the damage zone for fluid migration. At the micrometre-scale, the permeability structure has also been influenced by fault inversion. Petrophysical and petrographical analyses in the hanging wall damage zone show that microstructural changes due to faulting have enhanced the micrometre-scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore-lining chlorite morphology as a result of fault deformation. Consequently, inversion has subsequently improved the micrometre-scale permeability structure of the damage zone adjacent to the Castle Cove fault plane. Characterisation of the permeability structure adjacent to reverse-reactivated faults at a range of scales will aid with predicting fluid flow associated with inversion structures. Structural and geochemical analyses in the next two chapters of this thesis aim to understand how subsurface fluids flow and characterise the source, evolution, and migration pathways of fluids preserved in inverted fault zones. The geochemical evolution of fluids precipitated as calcite and siderite-cemented concretions and fractures throughout the eastern Otway Basin have been investigated. Pore fluids were sourced from both meteoric water and sea water during the deposition of the Eumeralla Formation and pore fluid evolution was strongly influenced by diagenetic reactions and increased temperature during burial. Using a similar analytical approach, the geochemical evolution of fluids precipitated as calcite and gypsum-cemented fractures throughout the eastern Bristol Channel Basin have vibeen investigated. The main source of fluids were connate pore waters, which were altered by diagenetic reactions within their host lithologies and subsequently redistributed through migration along faults and their associated damage zones. Knowledge of the source, evolution, and migration pathways of these fluids provides valuable insights for understanding the development of inverted sedimentary basins through time. Consequently, integrated studies on the multi-scaled permeability structure of inverted fault zones and the fluids preserved within them will ultimately improve fluid exploration and monitoring strategies in sedimentary basins.
Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum (ASP), 2019

Structures within very large displacement, mature fault zones, such as the North Branch San Gabriel Fault (NBSGF), are the product of a complex combination of processes. Off-fault damage within a damage zone and first-order geometric asperities, such as bends and steps, are thought to affect earthquake rupture propagation and energy radiation, but the effects are not completely understood. We hypothesize that the rate of accumulation of new damage decreases as fault maturity increases, and damage magnitude saturates in very large displacement faults. Nonetheless, geometric irregularities in the fault surface may modify damage zone characteristics. Accordingly, we seek to investigate the orientation, kinematics, and density of features at a range of scales within the damage zone adjacent to an abrupt 13 degree bend over 425 m in the NBSGF in order to constrain the relative role of the initiation of new damage versus the reactivation of preexisting damage adjacent to a bend. Field investigation and microstructural study focused on structural domains before, within, and after the fault bend on both sides of the fault. Subsidiary fault fabrics are similar in all domains outside the bend, which suggests a steady state fracture density and orientation distribution is established on the straight segments before and after the bend. The density of fractures within and outside the bend is similar; however, subsidiary fault orientations and kinematics are different within the bend relative to the straight segments. These observations are best explained by relatively low rates of damage generation relative to rates of fault reactivation during the later stages of faulting on the NBSGF, and that damage zone kinematics is reset as the host rock moves into the bend and again upon exiting the bend. Consequently, significant energy released during earthquake unloading can be dissipated by reactivation and slip on existing fractures in the damage zone, particularly adjacent to mesoscale faults. Thus, areas of heightened reactivation of damage, such as adjacent to geometric irregularities in the fault surface, could affect earthquake rupture dynamics.

abstract: The study of fault zones is a critical component to understanding earthquake mechanics and seismic hazard evaluations. Models or simulations of potential earthquakes, based on fault zone properties, are a first step in mitigating the hazard. Theoretical models of earthquake ruptures along a bi-material interface result in asymmetrical damage and preferred rupture propagation direction. Results include greater damage intensity within stiffer material and preferred slip in the direction of the more compliant side of the fault. Data from a dense seismic array along the Clark strand of the SJFZ at Sage Brush Flat (SGB) near Anza, CA, allows for analysis and characterization of shallow (<1km depth) seismic structure and fault zone properties. Results indicate potential asymmetric rock damage at SGB, similar to findings elsewhere along the SJFZ suggesting an NW preferred rupture propagation. In this study, analysis of high resolution topography suggests asymmetric morphology of the SGB basin slopes are partially attributed to structural growth and fault zone damage. Spatial distributions of rock damage, from site mapping and fault perpendicular transects within SGB and Alkali Wash, are seemingly asymmetric with pulverization dominantly between fault strands or in the NE fault block. Remapping of the SJFZ through Alkali Wash indicates the fault is not isolated to a single strand along the main geologic boundary as previously mapped. Displacement measurements within SGB are analogous to those from the most recent large earthquake on the Clark fault. Geologic models from both a 3D shear wave velocity model (a product from the dense seismic array analysis) and lithologic and structural mapping from this study indicate surface observations and shallow seismic data compare well. A synthetic three-dimensional fault zone model illustrates the complexity of the structure at SGB for comparison with dense array seismic wave products. Results of this study generally agree with findings from seismic wave interpretations suggesting damage asymmetry is controlled by a NW preferred rupture propagation.
Dissertation/Thesis
Geologic Map of Sage Brush Flat
3D fault zone model of the SJFZ at Sage Brush Flat
Masters Thesis Geological Sciences 2018

Spot core from the San Andreas Fault Observatory at Depth (SAFOD) borehole provides the opportunity to characterize and quantify damage and mineral alteration of siliciclastics within an active, large-displacement plate-boundary fault zone. Deformed arkosic, coarse-grained, pebbly sandstone, and fine-grained sandstone and siltstone retrieved from 2.55 km depth represent the western damaged zone of the San Andreas Fault, approximately 130 m west of the Southwest Deforming Zone (SDZ). The sandstone is cut by numerous subsidiary faults that display extensive evidence of repeating episodes of compaction, shear, dilation, and cementation. The subsidiary faults are grouped into three size classes: 1) small faults, 1 to 2 mm thick, that record an early stage of fault development, 2) intermediate-size faults, 2 to 3 mm thick, that show cataclastic grain size reduction and flow, extensive cementation, and alteration of host particles, and 3) large subsidiary faults that have cemented cataclastic zones up to 10 mm thick. The cataclasites contain fractured host-rock particles of quartz, oligoclase, and orthoclase, in addition to albite and laumontite produced by syn-deformation alteration reactions. Five structural units are distinguished in the subsidiary fault zones: fractured sandstones, brecciated sandstones, microbreccias, microbreccias within distinct shear zones, and principal slip surfaces. We have quantified the particle size distributions and the particle shape of the host rock mineral phases and the volume fraction of the alteration products for these representative structural units. Shape characteristics vary as a function of shear strain and grain size, with smooth, more circular particles evolving as a result of increasing shear strain. Overall, the particle sizes are consistent with a power law distribution over the particle size range investigated (0.3 µm < d < 400 µm). The exponent (fractal dimension, D) is found to increase with shear strain and volume fraction of laumontite. This overall increase in D and evolution of shape with increasing shear strain reflects a general transition from constrained comminution, active at low shear strains to abrasion processes that dominate at high shear strains.

Characterization of fractures in an arkosic sandstone from the western damage zone of the San Andreas Fault (SAF) at San Andreas Fault Observatory at Depth (SAFOD) was used to better understand the origin of damage and to determine the scale dependence of fracture fabric and fracture density. Samples for this study were acquired from core taken at approximately 2.6 km depth during Phase 1 drilling at SAFOD. Petrographic sections of samples were studied using an optical petrographic microscope equipped with a universal stage and digital imaging system, and a scanning electron microscope with cathodoluminescence (SEM-CL) imaging capability. Use of combined optical imaging and SEM-CL imaging was found to more successfully acquire true fracture density at the grain scale. Linear fracture density and fracture orientation were determined for transgranular fractures at the whole thin section scale, and intragranular fractures at the grain scale. The microscopic scale measurements were compared to measurements of mesoscopic scale fractures in the same core, as well as to published data from an ancient, exhumed trace of the SAF in southern California. Fracturing in the damage zone of the SAF fault follows simple scaling laws from the grain scale to the km scale. Fracture density distributions in the core from SAFOD are similar to distributions in damaged arkosic sandstone of the SAF along other traces. Transgranular fractures, which are dominantly shear fractures, indicate preferred orientation approximately parallel to the dominant sets of the mesoscale faults. Although additional work is necessary to confirm general applicability, the results of this work demonstrate that fracture density and orientation distribution over a broad range of scales can be determined from measurements at the mesoscopic scale using empirical scaling relations.

碩士
國立臺北科技大學
資源工程研究所
106
The northeastern coast of Taiwan is part of the northern extension of the Hsuehshan Range and has complex geological structures. The strata of Tatungshan formation from the Hsuehshan Range. Along the coast are dominated by drgillite and intercalated with thin layers of gray sandstone or siltstone. In this area, it is subject to regional tectonic action, with well developed fractures on the abrasion platform, which is by many strike-slip faults, resulting in intricate fracture patterns. This study adopts the concept of a fracture network (Sanderson and Nixon, 2015) utilizing the relationship of the fractures in the region to determine the type of fractures; there are different types of branches between nodes. There are six types of branch types and branching patterns, which describe the relationship between different nodes and further the order of development. The fault pattern is based on the geometry of the strike-slip fault zone (Kim et al., 2004). The fault geometry of the translational fault in this region is integrated. It is understood that the fault geometry corresponds to the location of the fault zone. The fractures in each area are staged through the depiction of the aerial photographs. At 113, at 114 and 116 km marks of the coastal road are divided into four stages of cracks; and the 115 km mark is divided into three stages of cracks. The integration of the fault zone can clearly use the fault geometry at different scales to make the comparison of the location of the fault zone; the branch type of this study may be I-I nodes as the first stage, the second stage as the I-Y nodes, the third stage is based on I-X, Y-Y and X-X nodes, and the fourth stage is based on I-Y nodes, where I,X and Y represent isolated, crossing and abutting nodes, repectively.

As hard rock mining progresses into higher stress mining conditions through either late stage extraction or mining at depth, the rock mass is driven not just to the peak strength, but often well into the post-peak until complete ‘failure’ occurs and easier mining conditions become evident. Limited research has been accomplished in identifying the transition of the rock mass and its behaviour into the post-peak and this research investigates this behaviour in detail. As the rock mass progressively fails, fractures are initiated through intact rock and extension and shear failure of these and pre-existing features occurs. Associated with this failure are microseismic events, which can be used to give an indication of the strength state of the rock mass. Based on an analogy to laboratory testing of intact rock and measurement of acoustic emissions, the microseismicity can be used to identify, fracture initiation, coalescence of fractures (yield), localization (peak-strength), accumulation of damage (post-peak) and ultimate failure (residual strength) leading to aseismic behaviour. The case studies presented in this thesis provide an opportunity to examine and analyse rock mass failure into the post-peak, through the regional and confined failures at the Williams and the Golden Giant mines, both in the Hemlo camp in Northern Ontario, Canada. At the Williams mine, the progressive failure of a sill pillar region into the post-peak was analysed; relating the seismic event density, combined with numerical modelling and a spatial and temporal examination of the principal components analysis (PCA), to characterize the extent, trend and state of the yielding zone, which formed a macrofracture shear structure. Observations of conventional displacement instrumentation, indicates regional dilation or shear of the rock mass occurs at or prior to the point of ‘disassociation’ (breakdown of stable PCA trends) when approaching the residual strength. At the Golden Giant mine, the complete process from initiation to aseismic behaviour is monitored in a highly stressed and confined pendent pillar. The PCA technique, numerical modelling and focal mechanism studies are used to define significant stages of the failure process, in which a similar macrofracture structure was formed. Temporal observations of key source parameters show significant changes prior to and at the point of coalescence and localization.