My research on fault zone structure has primarily focused on answering a few basic questions: does the zone of highly damaged rocks surrounding a fault (Fig.1) persist at depth, or can deep faults be modeled as relatively narrow and highly localized regions of slip? And if faults do become more localized at depth, what are the geometrical character and surrounding velocity structure of the localized surface? The answers to these questions have fundamental consequences and predictive power for earthquake rupture dynamics, radiation patterns, seismicity patterns, and ground motion prediction. In spite of their importance, we currently only have a few pieces of evidence to draw from in answering them. Observations by geologists are limited to only a handful of outcrops worldwide that represent faults which have been exhumed from seismogenic depths. By their very nature, these outcrops have undergone significant deformation in order to be observed at the surface today, and thus may not be representative of fault zone structure as it exists in situ.
Seismic waves propagating through fault zones provide us with direct evidence of fault zone structure (Fig. 2). However, traditional seismic tomography techniques suffer from three main limitations when applied to fault zones: standard body and surface waves have relatively low-resolution, travel time methods have decreasing ray sampling with grid size reduction, and detailed imaging requires enormous computing power. My research aims to overcome these obstacles by focusing on three specific goals: creating a database of fault-zone-sensitive seismic phases in addition to body and surface waves, employing adjoint waveform imaging with volumetric sensitivity kernels, and by making full use of supercomputing clusters.::: Under Construction :::