The Evolution of Fault Orientation in the 2019 Ridgecrest Earthquake Sequence with a New Long-Term Catalog of Seismicity and Moment Tensors

Abstract

Throughout an earthquake sequence, perturbations to the stress field may lead to changes in the distribution of active fault orientations. Resolving such changes for narrow spatiotemporal windows requires high-quality seismicity catalogs and objective techniques to measure fault orientations. We investigate the evolution of fault orientations throughout the 2019 Ridgecrest earthquake sequence using a new seismicity catalog that captures the sequence over several years. We generate this catalog using a state-of-the-art workflow for event detection, absolute and relative relocation, and moment tensor inversion. With this catalog, we measure high resolution, time-dependent changes in the orientations of active faults using a technique from spatial statistics that quantifies anisotropic features in point processes. We evaluate the results alongside those of more standard techniques based on focal mechanisms. Near the centroid of the mainshock, we observe a substantial shift in the distribution of fault orientations, whereas to the south of the mainshock centroid, we observe only a moderate transient change in the distribution of fault orientations. Compared with results derived from focal mechanisms alone, our findings suggest a smaller background differential stress and a distinct response of the stress state to postseismic deformation.

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