Seismic velocity structure of the Ridgecrest, CA region from traveltime tomography

Malcolm White


Date & Time
Online-only seminar via Microsoft Teams

We derive a local earthquake catalog and detailed 3D models of seismic P- and S-wave speeds (vP and vS, respectively) for the region around the 2019 Mw7.1 Ridgecrest earthquake in the Eastern California Shear Zone. The study uses traveltimes from aftershocks of the Mw7.1 Ridgecrest earthquake recorded by seventy-eight geophone sensors deployed rapidly in two rectangular arrays (Catchings et al., 2020) and seventy-four broadband seismometers from the regional network. The raw waveform data are first processed using automated procedures to detect and locate nearly 95,000 earthquakes--more than two and a half times the number of events reported by the published catalog of the Southern California Seismic Network (36,343 events). Over 2.47 x 106 P- and 1.52 x 106 S-wave arrival times are used in a new traveltime tomography method based on stochastic Voronoi-cell subspace projections of the model space (Fang et al., 2019) and a robust 3D ray tracer that uses the Fast Marching Method for solving the eikonal equation (White et al., 2020). The derived high-resolution vP, vS, and vP/vS models correlate closely with surface geology and spatial seismicity patterns. Salient features include (a) a volume of low vP, vS, and vP/vS material at the SE terminus of the Eastern Little Lake Fault (ELLF) where it abuts the Garlock Fault; (b) high vP/vS values characterizing the crust hosting the majority of aftershocks on the ELLF; and (c) low vP, low vS, and high vP/vS beneath the Coso Volcanic Field.

During Wednesday's seminar, I will describe our earthquake catalog, velocity models, and key methods used to derive them. Then I will interpret the velocity models in relation to spatial seismicity patterns and surface geology. Finally, I will speculate on potential relationships between seismicity patterns, velocity structure, and rupture dynamics.

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