Fault Zone Properties And Earthquake Rupture Dynamics

The dynamics of the earthquake rupture process are closely related to fault zone properties which the authors have intensively investigated by various observations in the field as well as by laboratory experiments. These include geological investigation of the active and fossil faults, physical and chemical features obtained by the laboratory experiments, as well as the seismological estimation from seismic waveforms. Earthquake dynamic rupture can now be modeled using numerical simulations on the basis of field and laboratory observations, which should be very useful for understanding earthquake rupture dynamics. Features: * First overview of new and improved techniques in the study of earthquake faulting * Broad coverage * Full color Benefits: * A must-have for all geophysicists who work on earthquake dynamics * Single resource for all aspects of earthquake dynamics (from lab measurements to seismological observations to numerical modelling) * Bridges the disciplines of seismology, structural geology and rock mechanics * Helps readers to understand and interpret graphs and maps Also has potential use as a supplementary resource for upper division and graduate geophysics courses.

Earthquakes are some of the most dynamic features of the Earth. This multidisciplinary volume presents an overview of earthquake processes and properties including the physics of dynamic faulting, fault fabric and mechanics, physical and chemical properties of fault zones, dynamic rupture processes, and numerical modeling of fault zones during seismic rupture. This volume examines questions such as: • What are the dynamic processes recorded in fault gouge? • What can we learn about rupture dynamics from laboratory experiments? • How do on-fault and off-fault properties affect seismic ruptures? • How do fault zones evolve over time? Fault Zone Dynamic Processes: Evolution of Fault Properties During Seismic Rupture is a valuable resource for scientists, researchers and students from across the geosciences interested in the earthquakes processes.

Considerable progress has been made recently in quantifying geometrical and physical properties of fault surfaces and adjacent fractured and granulated damage zones in active faulting environments. There has also been significant progress in developing rheologies and computational frameworks that can model the dynamics of fault zone processes. This volume provides state-of-the-art theoretical and observational results on the mechanics, structure and evolution of fault zones. Subjects discussed include damage rheologies, development of instabilities, fracture and friction, dynamic rupture experiments, and analyses of earthquake and fault zone data.

Using dynamic modeling of earthquake rupture on a strike-slip fault and seismic wave propagation in a three dimensional inhomogeneous elastoplastic medium, I investigate the inelastic response of compliant fault zones to nearby earthquakes. I primarily examine the plastic strain distribution within the fault zone and the displacement field that characterizes the effects of the presence of the fault zone. I find that when the fault zone rocks are close to failure in the prestress field, plastic strain occurs along the entire fault zone near the Earth's surface and some portions of the fault zone in the extensional quadrant at depth, while the remaining portion deforms elastically. Plastic strain enhances the surface displacement of the fault zone, and the enhancement in the extensional quadrant is stronger than that in the compressive quadrant. These findings suggest that taking into account both elastic and inelastic deformation of fault zones to nearby earthquakes may improve our estimations of fault zone structure and properties from small-scale surface deformation signals. Furthermore, identifying the inelastic response of nearby fault zones to large earthquakes may allow us to place some constraints on the absolute stress level in the crust. I also investigate how to distinguish inelastic and elastic responses of compliant fault zones to the nearby rupture. I explore in detail the range of plastic parameters that allow plastic strain to occur and examine its effect on the displacement field around compliant fault zone. I find that the sympathetic motion (i.e., consistent to long-term geologic slip) or the reduced retrograde motion (i.e., opposite to long-term geologic slip) observed in residual displacement on fault parallel horizontal direction can be directly used to distinguish the inelastic deformation from the elastic deformation. This may help better interpret the geodetic observations in the further. In addition, I conduct models with various fault zone geometries (i.e., depth, width and shape) and rigidity reduction properties to test their effects on the displacement field. The results from elastic models suggest that to the same dynamic rupture source, the deeper and wider pre-existing nearby fault zone will result in larger residual displacement. But this only applies to fault zones with large depth extent. For shallow fault zones, residual displacement tends to keep the same magnitude or even decreases with fault zone width. While in plastic models, where plastic strain is allowed, displacement field is more complex. The magnitude of the residual displacement will be enhanced by the occurrence of plastic strain. Then I extend the theoretical simulations of an idealized planar rupture fault system into one in a geometrically complex real fault system in the East California Shear Zone (ECSZ). I compare our simulation results of the 1992 Landers Earthquake with the geodetic observations. Responses of the Calico and Rodman compliant fault zone are better understood by taking into account of both inelastic and elastic responses of compliant fault zones to the nearby Landers rupture. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152529

This book is devoted to different aspects of earthquake research. Depending on their magnitude and the placement of the hypocenter, earthquakes have the potential to be very destructive. Given that they can cause significant losses and deaths, it is really important to understand the process and the physics of this phenomenon. This book does not focus on a unique problem in earthquake processes, but spans studies on historical earthquakes and seismology in different tectonic environments, to more applied studies on earthquake geology.

Previous models of earthquake rupture dynamics have neglected interesting deformational properties of fault zone materials. While most current studies involving off-fault inelastic deformation employ simple brittle failure yield criteria such as the Drucker-Prager yield criterion, the material surrounding the fault plane itself, known as fault gouge, has the tendency to deform in a ductile manner accompanied by compaction. We incorporate this behavior into a new constitutive model of undrained fault gouge in a dynamic rupture model. Dynamic compaction of undrained fault gouge occurs ahead of the rupture front. This corresponds to an increase in pore pressure which preweakens the fault, reducing the static friction. Subsequent dilatancy and softening of the gouge causes a reduction in pore pressure, resulting in fault restrengthening and brief slip pulses. This leads to localization of inelastic failure to a narrow shear zone. We extend the undrained gouge model to a study of self-similar rough faults. Extreme compaction and dilatancy occur at restraining and releasing bends, respectively. The consequent elevated pore pressure at restraining bends weakens the fault and allows the rupture to easily pass, while the decrease in pore pressure at releasing bends dynamically strengthens the fault and slows rupture. In comparison to other recent models, we show that the effects of fault roughness on propagation distance, slip distribution, and rupture velocity are diminished or reversed. Next, we represent large subduction zone megathrust earthquakes with a dynamic rupture model of a shallow dipping fault underlying an accretionary wedge. In previous models by our group [Ma, 2012; Ma and Hirakawa, 2013], inelastic deformation of wedge material was shown to enhance vertical uplift and potential tsunamigenesis. Here, we include a shallow region of velocity strengthening friction with a rate-and-state framework. We find that coseismic increase of the basal friction drives further inelastic wedge failure in comparison with our previous models, with the implication of larger tsunami generation.

Professor Richard (Rick) Sibson revolutionized structural geology by illustrating that fault rocks contain an integrated record of earthquakes. Fault-rock textures develop in response to geological and physical variables such as composition, environmental conditions (e.g. temperature and pressure), fluid presence and strain rate. These parameters also determine the rate- and state-variable frictional stability of a fault, the dominant mineral deformation mechanism and shear strength, and ultimately control the partitioning between seismic and aseismic deformation. This volume contains a collection of papers that address the geological record of earthquake faulting from field-based or theoretical perspectives.

A major update of this classic reference text on earthquakes and faulting with a wealth of new topics and observations.