Thesis (Ph. D.)--Oregon State University, 1995. / Typescript (photocopy). Includes bibliographical references (leaves 119-130). Also available on the World Wide Web.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

The geometry and mineralization features of small left-lateral strike-slip faults and associated fractures in Lake Edison Granodiorite of the central Sierra Nevada, California, were examined in order to model the three-dimensional structure of strike-slip faults. These faults, which are reactivated joints, were also examined to determine fault sizes, starting joint size, and evidence for fluid flow. The associated secondary fractures are usually found in the dilational quadrants of fault-tip regions. The longest fault-segment trace is 32.14 m; the longest joint trace is 22 m. The joint population length (l) is represented by a power-law distribution (l-n) and it is l-1.22. The fault-segment distributions are l-0.23~0.79, and the compiled fault-segment distribution is l-1.18. The data on fracture and fault spacing, along with the joint power-law distribution, will aid in the simulation and analysis of fault evolution. The splay-fracture traced in the faults are linear at depth and the average splay-fracture angle is 39° ± 13°. The dihedral angle of the splay plane and fault plane ranges from 20° to 65°. There is a high concentration of splay fractures near the fault. As distance increases perpendicular form the fault, the splay-fracture spacing increases and splay-fracture frequency decreases. The splay tracelength distributions have a high short tracelength concentration with a rapid decrease of long tracelengths. The maximum tracelength of multiple splay-fracture groups is restricted by their distance orthogonal to the fault trace. The three-dimensional relationship between the splay-fracture plane and fault plane can be inferred from these data. When present, mineralized quartz appears largely as lenses and few as single continuous veins along the faults. No consistent pattern exists between fault displacement and the locations and dimensions of quartz cavities. There is no visible damage zone near the fault termination or around the faults. Microstructures in the fault zone consist of cataclasites and patchy gouges, and zones of dynamically recrystallized fault walls. The three-dimensional geometry, along with quartz cavity distribution and thin section analysis, has led to the conclusion that fluid migrates vertically among the faults and fractures.

The main objective of this work is to test the effect of two conical-shaped positive topographic obstacleson propagation of a discrete basement dextral strike-slip or transcurrent fault. A set of sandbox analogue (physical) models was constructed, in which two consecutive sand cones were placed progressivelycloser to each other. Key structural and strain parameters, such axial strain ratios and angular strain, aswell as the width and direction of the basins which formed during deformation were measured and analyzed. This procedure was then repeated with a basal decoupling layer of PDMS beneath each cone,to test the influence of this layer on the deformation.The results show that, for models without a basal decoupling layer, the distance between the two cones governs the end-stage deformation patterns of the topographic obstacles. The proximity of the topographic obstacles causes an increase of their deformation, i.e., results in higher axial strain ratios and angular strain. This effect is particularly noticeable in the first obstacle, which is affected by a strong clockwise rotation. The basal ductile which partly decouples the basement fault from the cover units nullifies the previous effect (the increase in deformation caused by proximity) and, when present, localizes the deformation by not only producing narrower pull-apart basins within the obstacles but alsoby increasing their rotation. / O objectivo deste trabalho foi o de estabelecer os efeitos de uma única falha de desligamento direito emdois obstáculos cónicos consecutivos, de relevo positivo. Adicionalmente, procura-se estabelecer o efeito que uma camada basal dúctil poderá ter na deformação dos obstáculos.Como tal, uma série de modelos análogos foram efetuados onde dois cones de areia consecutivosforam colocados sistematicamente mais próximos um do outro. Durante estas experiências, parâmetros chave de natureza estrutural e de strain foram medidos, tais como os rácios de strain axial e angular,bem como a direção e largura das bacias formadas. Este procedimento foi repetido com uma camadabasal de silicone (PDMS) colocada por baixo dos obstáculos. Os resultados mostram que, para modelos sem a camada de silicone basal, a distância de separação dos cones tem uma influência muito forte no produto final da deformação nos cones. A proximidade dos obstáculos causa um aumento da deformação (ex. valores mais elevados de strain angular e strain axial) em ambos os obstáculos. Este efeito é particularmente visível no primeiro obstáculo, sendo este afetado por uma rotação no sentido dos ponteiros do relógio mais elevada que o segundo.Por fim, verifica-se que a presença da camada basal dúctil nulifica o efeito anterior e, quando presente, focaliza a deformação, não só criando bacias de pull-apart mais estreitas mas tambémcausando uma maior rotação nos obstáculos.

The styles of deformation of the fore-arc wedges along the Chilean convergent margin are observed to vary significantly, despite similar plate kinematic conditions. Here, I focus on the analysis of fore-arc deformation on two regions along the Chilean convergent margin at 20°-24°S and 37°-42°S. Although both regions are subjected to the oblique subduction of the oceanic Nazca plate and backstopped by the Andes mountain chain; they display different patterns of deformation. The northern Chilean study area (20° - 24°S) is characterized by an exceptionally thick crust of about 60 km beneath the Altiplano – Puna plateau, lack of an accretionary wedge in the fore-arc due to hyperarid climate, and consequently a sediment starved trench. Two major margin parallel strike slip faults are observed in this area, the Atacama Fault Zone (AFZ) and the Precordilleran Fault System (PFS). Both strike-slip faults do not exhibit significant recent displacement. The southern study area (37° - 42°S), compared to the northern study area, is characterized by lower topography, high precipitation rates (~2000 mm/yr), and a younger subducted oceanic plate. An active strike-slip fault, the Liquiñe-Ofqui-Fault-Zone (LOFZ), shows ~1 cm/yr recent dextral movement and shapes the surface of this area. Thus, the southern Chilean study area exhibits localized strike-slip motion. Within this area the largest earthquake ever recorded, the 1960 Valdivia earthquake, occurred with a moment magnitude of MW=9.5. I have constructed 2D thermal models and 3D mechanical models for both Chilean study areas to study processes related to active subduction. The applied numerical method is the finite element technique by means of the commercial software package ABAQUS. The thermal models are focused on the thermal conditions along the plate interface. The thermal structure along the plate interface reveals the limits of coupling but also the type of transition from coupled to uncoupled and vice versa. The model results show that shear heating at the plate interface is an important mechanism that should be taken into account. The models also show that the thermal condition at the downdip limit of the coupling zone leads to a sharp decrease of friction along the interface. Due to the different geometries of the two Chilean study areas, such as the slab dip and the thickness of the continental crust, the downdip limit of the southern study area is slightly shallower than that of the northern study area. The results of the 2D thermal models are used to constrain the spatial extent of the coupling zone in the 3D mechanical models. 3D numerical simulations are used to investigate how geometry, rheology and mechanical parameters influence strain partitioning and styles of deformation in the Chilean fore-arc. The general outline of the models is based on the fore-arc geometry and boundary conditions as derived from geophysical and geological field data. I examined the influence of different rheological approaches and varying physical properties of the fore-arc to identify and constrain the parameters controlling the difference in surface deformation between the northern and southern study area. The results of numerical studies demonstrate that a small slab dip, a high coefficient of basal friction, a high obliquity of convergence, and a high Young’s modulus favour localisation of deformation in the fore-arc wedge. This parameter study helped me to constrain preferred models for the two Chilean study areas that fit to first order observations. These preferred models explain the difference in styles of deformation as controlled by the angle of obliquity, the dip of subducting slab, and the strength of wedge material. The difference in styles can be even larger if I apply stronger coupling between plates within the southern area; however, several independent observations indicate opposite tendency showing southward decrease of intensity of coupling. The weaker wedge material of the preferred model for the northern study area is associated with advanced development of the adjacent orogen, the Central Andes. Analysis of world-wide examples of oblique subduction zones supports the conclusion that more mature subduction zones demonstrate less pronounced localization of strike-slip motion. / Die Deformationsmuster der Fore-Arc Keile entlang des chilenischen konvergenten Plattenrandes variieren beachtlich, trotz ähnlicher plattenkinematischer Randbedingungen. In dieser Arbeit konzentriere ich mich auf die Analyse der Deformation des Fore-Arcs in zwei Gebieten entlang des chilenischen konvergenten Plattenrandes zwischen 20°-24°S und 37°-42°S. Obwohl beide Gebiete durch schiefe Subduktion der ozeanischen Nazca Platte und der östlichen Begrenzung durch die Andine Gebirgskette gekennzeichnet sind, zeigen sie unterschiedliche Deformationsmuster an der Oberfläche. Das nördliche chilenische Gebiet (20° - 24°S) ist gekennzeichnet durch eine außergewöhnliche Krustendicke von ~ 60 km unterhalb des Altiplano - Puna Plateaus, dem Fehlen eines akkretionären Prismas im Fore-Arc aufgrund des trockenen Klimas und somit einer nahezu sedimentfreien Tiefseerinne. Zwei große Plattenrand-parallele Strike-Slip Störungen werden in diesem Gebiet beobachtet, die Atacama Fault Zone (AFZ) und das Precordilleran Fault System (PFS). Beide Strike-Slip Störungen zeigen keine signifikanten aktuellen Bewegungsraten. Das südliche Gebiet (37° - 42°S) ist im Vergleich zum nördlichen Gebiet durch eine niedrigere Topographie, hohe Niederschlagsraten (~2000 mm/a) und eine jüngere abtauchende ozeanische Platte gekennzeichnet. Die aktive Strike-Slip Störung, Liquiñe-Ofqui-Fault-Zone (LOFZ), ist gekennzeichnet durch aktuelle dextrale Bewegungsraten von 1 cm/a und prägt die Oberflächenstruktur in dieser Region. Folglich ist der südliche Arbeitsbereich durch lokalisierte Strike-Slip Bewegung charakterisiert. Innerhalb dieses Gebietes ereignete sich das größte instrumentell aufgezeichnete Erdbeben, das 1960 Valdivia Erdbeben, mit einer Stärke von MW=9.5. 2D thermische Modelle und 3D mechanische Modelle wurden für die beiden chilenischen Gebiete konstruiert, um Prozesse im Zusammenhang mit aktiver Subduktion zu untersuchen. Als numerisches Verfahren wurde die Finite Elemente Methode mit Hilfe des kommerziellen Softwarepakets ABAQUS angewandt. Die thermischen Modelle sind auf die thermischen Konditionen entlang der Plattengrenzfläche fokussiert. Die thermische Struktur entlang der Plattengrenzfläche zeigt die Grenzen der Kopplung an aber auch die Art des Überganges von gekoppelt zu nicht gekoppelt und umgekehrt. Die Modellergebnisse zeigen, dass Heizen infolge der Scherung an der Plattengrenzfläche ein wichtiger Faktor ist, der in Betracht gezogen werden sollte. Die Modelle zeigen auch, dass die thermische Struktur an der unteren Begrenzung der Koppelzone zu einer deutlichen Abnahme der Reibung entlang der Grenzfläche führt. Aufgrund der unterschiedlichen Geometrien der zwei chilenischen Untersuchungsgebiete, z.B. Abtauchwinkel der ozeanischen Platte und Krustendicke, ist die untere Begrenzung der Koppelzone des südlichen Untersuchungsgebietes in geringerer Tiefe als die des nördlichen Gebietes. Die Ergebnisse der thermischen 2D Modelle werden genutzt, um die räumliche Ausdehnung der Koppelzone in den mechanischen 3D Modellen festzulegen. Numerische 3D Simulationen werden genutzt, um zu verstehen, wie Geometrien, Rheologien und mechanische Parameter die Verformungspartitionierung und das Deformationsmuster im chilenischen Fore-Arc beeinflussen. Ich habe den Einfluss unterschiedlicher rheologischer Ansätze und unterschiedlicher physikalischer Eigenschaften auf den Fore-Arc untersucht, um Parameter zu identifizieren und zu bestimmen, die den Unterschied des Deformationsmusters zwischen dem nördlichen und südlichen Gebiet steuern. Die Ergebnisse der numerischen Studien stellen heraus, dass ein kleinerer Abtauchwinkel der ozeanischen Platte, ein hoher basaler Reibungskoeffizient, eine hohe Konvergenzschiefe und ein großer Elastizitätsmodul die Lokalisierung der Deformation im Fore-Arc Keil begünstigen. Basierend auf dieser Parameterstudie habe ich Modelle für die beiden chilenischen Gebiete ausgewählt, die in Beobachtungen erster Ordnung übereinstimmen. Diese ausgewählten Modelle erklären die unterschiedlichen Deformationsmuster durch eine größere Konvergenzschiefe, einen kleineren Abtauchwinkel der ozeanischen Platte und ein härteres Keilmaterial für das südliche Untersuchungsgebiet. Der Unterschied bezüglich der Deformationsmuster kann sogar größer sein, wenn ich eine größere Reibung zwischen den Platten im südlichen Gebiet anwende; jedoch zeigen einige unabhängige Beobachtungen eine umgekehrte Tendenz: eine Abnahme der Intensität der Koppelung von Nord nach Süd. Das schwächere Keilmaterial des ausgewählten Modells für das nördliche Untersuchungsgebiet steht im Zusammenhang mit der fortgeschrittenen Entwicklung des angrenzenden Orogens, der zentralen Anden. Die Analyse weltweiter Beispiele von schiefen Subduktionzonen unterstützt die Schlussfolgerung, dass ältere Subduktionzonen weniger ausgeprägte Lokalisierung von Strike-Slip Bewegung aufzeigen.

Le système de failles de Haiyuan qui borde le plateau du Tibet au Nord-Est est un système majeur sénestre. Au cours du dernier siècle, deux grands séismes (M~8) ont rompu ce système de failles: le séisme de Haiyuan en 1920 et le séisme de Gulang en 1927. A l'aide d'interférométrie radar à synthèse d'ouverture, nous analysons les variations spatiales et temporelles de la déformation intersismique au travers de la faille de Haiyuan, dans une zone étendue (150x150 km2) qui couvre l'extrémité Ouest de la rupture de 1920 et la lacune sismique de Tianzhu. Avec une approche dite en Small Baseline, nous traitons cinq séries temporelles d'images SAR, acquises par le satellite Envisat le long de tracks descendantes et ascendantes pendant la période allant de 2003 à 2009. Les cartes de vitesse moyenne de déformation dans la ligne de visée du satellite ainsi obtenues sont cohérentes avec un mouvement sénestre au travers de la faille et montrent des variations latérales du gradient de vitesse dans la zone de faille. Nous inversons ces cartes de vitesse moyenne en LOS pour obtenir le taux de chargement à court terme en profondeur et la distribution du glissement dans la partie sismogène le long du plan de faille. Le taux de chargement en profondeur est d'environ 5mm/an. Les sections de faille ayant rompu en 1920 et une grande partie de la lacune sismique de Tianzhu sont bloquées en surface. Entre ces deux sections, un segment de 35 km de long, qui montre une forte activité micro-sismique, glisse de manière asismique avec un taux de glissement horizontal qui atteint presque 5 mm/an. Cependant, le taux de glissement asismique le long de la partie sismogène varie le long du plan de faille et atteint localement des taux supérieurs au chargement tectonique, suggérant des variations temporelles du glissement asismique. La comparaison de profils moyens de vitesse parallèle à la faille issus de données InSAR sur les périodes 1993-1998 (données ERS) et 2003-2009 suggèrent une migration vers la surface du glissement asismique sur une période de 20~ans. Une analyse en séries temporelles des données Envisat, en appliquant un lissage temporel, montrent une accélération du taux de glissement asismique pendant l'année 2007. Cette accélération est précédée et a probablement été déclenchée par un séisme de magnitude 4.7 au sein même du glissement asismique. Enfin, nous étudions la relation entre l'évolution spatio-temporelle du glissement asismique en surface et la rugosité de la trace de la faille à l'aide d'une analyse multi-échelle. Nous montrons que les propriétés élastiques de la croûte cassante contrôlent la rugosité de la faille, qui exerce à son tour un contrôle sur la distribution de glissement asismique en surface. Le glissement asismique est fait de spasmes qui interagissent les uns avec les autres en suivant une loi d'échelle similaire à la loi de Gutenberg-Richter pour les séismes. / The Haiyuan fault system is a major left-lateral fault system bounding the tibetan plateau to the north-east. Two M~8 earthquakes ruptured that fault system in the past hundred years: the 1920, Haiyuan earthquake and the 1927, Gulang earthquake. Here, we use Synthetic Aperture Radar interferometry to explore the spatial and temporal variations of the interseismic deformation across the Haiyuan fault, over a broad (150x150 km2) area covering the 1920 rupture zone and the millennial Tianzhu seismic gap. Using a small baseline approach, we process five SAR images time series acquired by the Envisat satellite along descending and ascending orbits, spanning the 2003-2009 period. The resulting mean Line-Of-Sight velocity maps are, in overall, consistent with left-lateral motion across the fault and reveal lateral variations of the velocity gradient in the near fault zone. We invert these mean LOS velocity maps for the short-term loading rate on the fault plane at depth and for the shallow slip distribution along the seismogenic part of the fault. The short-term loading rate is about 5 mm/yr. The shallow sections of the fault, that ruptured in 1920 and the most part of the Tianzhu seismic gap are currently locked. In between, a 35 km-long section, that experiences a strong micro-seismic activity, is creeping at a mean horizontal rate of almost 5 mm/yr. However, the shallow creep rate varies along the fault strike and locally reaches values higher than the deep loading rate. This suggests temporal fluctuations of the observed aseismic slip. The comparison of InSAR-derived averaged profiles of the fault parallel velocity, spanning the 1993-1998 (ERS data) and 2003-2009 periods, suggests an upward migration of the creep over the 20 years-long observation period. A time series analysis on the Envisat dataset using a temporal smoothing reveals a creep rate increase during the year 2007. This rate increase follows and may have been triggered by a M4.7 earthquake that occurred on the creeping patch. We finally investigate the relationship between the spatio-temporal evolution of the surface creep and the roughness of the surface fault trace with a multiscale analysis. We show the control of the elastic properties of the brittle crust on the fault roughness, that in turn exerts a direct control on the surface aseismic slip distribution. The aseismic slip is made of locally interacting bursts that follow a scaling law similar to the Gutenberg-Richter law for earthquakes.

Le Venezuela est traversé par une zone de limite de plaque. Ce système tectonique accommode les mouvements relatifs de trois plaques majeures: la plaque Sud-Américaine, la plaque Caraïbe et la plaque de Nazca. Ce système est constitué de failles décrochantes actives qui ont généré au Venezuela de nombreux séismes de magnitude supérieure à 6-7. Parmi ces failles, cette thèse se focalise sur la faille de Boconó et la faille d’El Pilar.Le but de cette thèse est d'étudier l'activité de ces failles sur plusieurs échelles de temps en utilisant une approche multidisciplinaire qui combine analyses morphotectonique, paléosismologique et géodésique. Cette approche a permis de préciser le régime de déformation de ces failles indispensable à l'estimation de l'aléa sismique.Antérieurement à cette thèse, dans la région de Yaracuy, l’activité tectonique du segment nord de la faille de Boconó était mal contrainte faute de données géodésiques ou géochronologiques suffisantes. Or cette partie de la faille a provoqué en 1812 un séisme de Mwi 7.4 qui a détruit les villes de la région.Grâce à la datation par Béryllium-10 de la surface d’exposition de cônes alluviaux décalés par la cinématique dextre de la faille, cette thèse montre que la vitesse quaternaire de la faille est comprise entre 5.0 et 11.2 mm/an.En comparant cette vitesse estimée sur ~ 200 ka et le taux de glissement estimé en champ lointain par des mesures géodésiques (~ 12 mm/an), il peut être proposé que la faille de Boconó accommode une grande partie de l'extrusion du Bloc Nord Andin. La réalisation de carte de vitesses moyennes de déformation à partir d'images SAR a montré l'absence de glissement asismique le long de la faille de Boconó entre 2007 et 2011. En extrapolant ce comportement aux derniers 200 ans, il en résulte que, depuis le dernier séisme en 1812 il y a une accumulation de déficit de glissement de quelques mètres selon la vitesse de glissement considérée. Cette faille représente donc un aléa sismique important pour la région. Une tranchée réalisée pour préciser cet aléa a montré que trois évènements sismiques de Mw > 6-6.5 ont lieu depuis 1300 ap. J.-C., le dernier de ces événements étant probablement le séisme historique de 1812.Au Nord Est du Venezuela, la faille d’El Pilar accommode l’intégralité du mouvement relatif entre la plaque Sud-Américaine et la plaque Caraïbe (~ 20 mm/an). Après le séisme de Ms 6.8 en 1997, le segment émergé de cette faille a subit un important « afterslip ». Des mesures géodésique réalisées en 2003, 2005 et 2013 ont montré que ce segment glisse encore asismiquement (~12 – 13 mm/an). Cette thèse présente une carte des vitesses de déformation entre 2007 et 2011 calculée par interférométrie radar. Celle-ci a permis de montrer que cette faille glisse asismiquement de façon non uniforme dans l’espace et le temps. L’analyse en série temporelle des déplacements a révélé que le glissement asismique de certains tronçons de la faille subit une accélération en Juin 2009 avec des vitesses de glissement asismiques supérieures au déplacement relatif entre les plaques. Cette observation permet d’interpréter que le glissement asismique a un comportement transitoire, en effet, des périodes de blocage et des périodes de larges glissements se succèdent. Cette succession doit probablement se poursuivre tout le long de la période intersismique comme le suggèrent le faible nombre de séismes historiques et préhistoriques au regard de la vitesse de coulissage le long de la faille. Enfin ce glissement asismique présentant des variations spatiales et temporelles est probablement contrôlé par la présence de serpentinites et d’une activité hydrothermale le long de la zone de faille, contexte connu pour favoriser des comportements rhéologiques de ce type. / Venezuela is crosscut by a plate boundary zone, this tectonic setting accommodates the relative displacements of three plates: the South America, the Caribbean and the Nazca Plate. This tectonic system is constituted of active strike-slip faults which have provoked several events of Mw > 6-7. Among these faults, this thesis focuses on the Boconó Fault and on the El Pilar Fault.The aim of this dissertation is to study fault activities on several time scales using a multidisciplinary approach. This approach, which combines morphotectonic, paleoseismologic and geodetic analyses, leads to clarify the deformation pattern. This knowledge is essential to the seismic hazard assessment.Previously to this thesis, in the Yaracuy valley, the tectonic activity of the Boconó fault was poorly constrained due to the lack of geodetic and geochronological data; although a part of this fault triggered in 1812 an earthquake of Mwi 7.4. Through 10-Beryllium surface exposition dating of two alluvial fans shifted by the fault, this thesis shows that the Quaternary slip rate of the fault ranges from 5.0 to 11.2 mm/yr. By comparing this rate estimated on ~ 200 ka with the slip rate estimated in far field with geodesy (~ 12 mm/yr), it can be proposed that the Boconó fault accommodates a major part of the North Andean Block extrusion. Velocity map of ground displacements calculated using SAR images shows the lack of aseismic slip along the Boconó Fault during the 2007-2011 period. The extrapolation of this locked activity since the 1812 event, implies that there is a slip deficit of several meters. Therefore, the Boconó Fault have to be taken into account in the regional seismic hazard assessment. A paleoseismological trench across the studied segment is also presented in this thesis in order to constrain this assessment. Three events of Mw > 6 - 6.5 have been recorded in this trench since 1300 CE, the last of these events is probably the 1812 historical earthquake.In the north-western region of Venezuela, the El Pilar Fault accommodates the whole relative displacement between South-America and Caribbean Plates (~ 20 mm/yr). After the last event in 1997 (Ms 6.8) the on-shore segment of this fault undergoes an important afterslip. Geodetic campaign measurements performed in 2003, 2005 and 2013 showed that this segment was still creeping (~ 12 - 13 mm/yr). This thesis presents an InSAR analysis performed with 18 SAR images spanning the 2007-2011 period. The velocity map shows that the aseismic slip is not uniform along the El Pilar Fault. Time-series analysis reveals locally a creep acceleration. This transient is characterised by a rate exceeding the rate of surrounding plate motion. Therefore, the El Pilar fault seems to be partially locked during several years and then undergoes transient creep during several months. This succession should last during the whole interseismic period as suggested by the low seismic activity and paleoseismological trenches. This creep showing spatio-temporal variations is probably controlled by the existence of serpentinites lenses and the hydrothermal activity, which are known to promote this kind of rheological behaviour.

The Clark fault is one of the primary dextral faults in the San Jacinto fault zone system, southern California. Previous mapping of the Clark fault at its southern termination in the San Felipe Hills reveals it as a broad right lateral shear zone that ends north of the crossing, northeast-striking, left-lateral Extra fault. We investigate the relationship between the dextral Clark fault and the sinistral Extra fault to determine whether the Clark fault continues to the southeast. We present new structural, geophysical and geomorphic data that show that the Extra fault is a ~7 km wide, coordinated fault array comprised of four to six left-lateral fault zones. Active strands of the Clark fault zone persists through the Extra fault array to the Superstition Hills fault in the subsurface and rotate overlying sinistral faults in a clockwise sense. New detailed structural mapping between the San Felipe and Superstition Hills confirms that there is no continuous trace of the Clark fault zone at the surface but the fault zone has uplifted an elongate region ~950 km. sq. of latest Miocene to Pleistocene basin-fill in the field area and far outside of it. Detailed maps and cross sections of relocated microearthquakes show two earthquake swarms, one in 2007 and another in 2008 that project toward the San Felipe Hills, Tarantula Wash and Powerline strands of the dextral Clark fault zone in the San Felipe Hills, or possibly toward the parts of the Coyote Creek fault zone. We interpret two earthquake swarms as activating the San Jacinto fault zone beneath the Extra fault array. These data coupled with deformation patterns in published InSAR data sets suggest the presence of possible dextral faults at seismogenic depths that are not evident on the surface. We present field, geophysical and structural data that demonstrate dominantly left-lateral motion across the Extra fault array with complex motion on secondary strands in damage zones. Slickenlines measured within three fault zones in the Extra fault array reveal primarily strike-slip motion on the principal fault strands. Doubly-plunging anticlines between right-stepping en echelon strands of the Extra fault zone are consistent with contraction between steps of left-lateral faults and are inconsistent with steps in dominantly normal faults. Of the 21 published focal mechanisms for earthquakes in and near the field area, all record strike-slip and only two have a significant component of extension. Although the San Sebastian Marsh area is dominated by northeast-striking leftlateral faults at the surface, the Clark fault is evident at depth beneath the field area, in rotated faults, in microseismic alignments, and deformation in the Sebastian uplift. Based on these data the Clark fault zone appears to be continuous at depth to the Superstition Hills fault, as Fialko (2006) hypothesized with more limited data sets.

Thesis (Ph. D.)--Dept. of Geosciences and School of Computing and Engineering. University of Missouri--Kansas City, 2005. / "A dissertation in geosciences and computer networking." Advisor: Tina M. Niemi. Typescript. Vita. Description based on contents viewed Mar. 12, 2007; title from "catalog record" of the print edition. Includes bibliographical references (leaves 331-341). Online version of the print edition.

Nine west-northwest-trending faults on the continental margin of Oregon and Washington, between 43° 05'N and 470 20'N latitude, have been mapped using seismic reflection, sidescan sonar, submersibles, and swath bathymetry. Five of these oblique faults are found on both the Juan de Fuca and North American plates, and offset abyssal plain sedimentary units left-laterally from 2.0 to 5.5 km. These five faults extend 8-18 km northwestward from the deformation front. The remaining four faults, found only on the North American plate, are also inferred to have a left-lateral slip sense. The age of the Wecoma fault on the abyssal plain is 600±50 ka, and has an average slip rate of 7-1 0 mm/year. Slip rates of the other four abyssal plain faults are 5.5 ± 2 - 6. 7 ± 3 mm/yr. These faults are active, as indicated by offset of the youngest sedimentary units, surficial fault scarps, offsets of surficial channels, and deep fluid venting. All nine faults have been surveyed on the continental slope using SeaMARC 1A sidescan sonar, and three of them were surveyed with a high-resolution AMS 150 sidescan sonar on the continental shelf off central Oregon. On the continental slope, the faults are expressed as linear, high-angle WNW trending scarps, and WNW trending fault-parallel folds that we interpret as flower structures. Active structures on the shelf include folds trending from NNE to WNW and associated flexural slip thrust faulting; NNW to N trending right-lateral strike-slip faults; and WNW trending left-lateral strike-slip faults. Some of these structures intersect the coast and can be correlated with onshore Quaternary faults and folds, and others are suspected to be deforming the coastal region. These structures may be contributing to the coastal marsh stratigraphic record of co-seismic subsidence events in the Holocene. We postulate that the set of nine WNW trending left-lateral strike-slip faults extend and rotate the forearc clockwise, absorbing most or all of the arc parallel component of plate convergence. The high rate of forearc deformation implies that the Cascadia forearc may lack the rigidity to generate M > 8.2 earthquakes. From a comparison of Cascadia seismogenic zone geometry to data from circum-Pacific great earthquakes of this century, the maximum Cascadia rupture is estimated to be 500 to 600 km in length, with a 150-400 km rupture length in best agreement with historical data. / Graduation date: 1994