Project Abstract
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Studies under this project focused on understanding the behavior of dynamic ruptures in geologically-relevant settings, clarifying properties of off-fault yielding for different fault and bulk rheologies, and improving the ability of inferring from field observations on persistent behavior of earthquake ruptures associated with individual fault sections. Toward these goals we worked on the following two research directions. (1) Detailed parameter-space study of properties of generated off-fault yielding (e.g., locations, extent, intensity, symmetry properties, microcrack orientations, decay with distance) for various conditions (e.g., different friction and bulk rheology parameters, different orientations of maximum compressive stress relative to the fault, different values of seismic S ratio and conditions representing various depth sections, velocity contrast across the fault). The results help developing correlations and scaling among different manifestations of off-fault yielding, and improve the understanding of generation of synthetic and antithetic faults (or R1-R2 Riedel shears) around the main fault ruptures, along with susceptibility of propagation along fault branches and bends at different angles. (2) Analysis of volumetric deformation structures near ends of fault segments, with a focus on small-scale features with opposite polarity to the expected larger-scale classical structures that may reflect arrest phases of ruptures. The results on topic (1) provide improved guidelines for interpreting various observed properties of rock damage near faults in terms of the generating mechanisms and regional/local stress fields. The results on topic (2) increase the type of field signals that can be used to infer likely propagation direction of large ruptures on a given fault section. |
