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Deep seismic velocity changes following the 2019 Ridgecrest earthquake

Jared T. Bryan, William B. Frank, & Pascal Audet

Submitted September 10, 2023, SCEC Contribution #13084, 2023 SCEC Annual Meeting Poster #043

The 2019 Ridgecrest earthquake sequence marks the largest seismic event in Southern California in over 20 years. Information on stress and damage evolution throughout the fault zone is necessary for understanding the dynamics of the event. Noise-based methods for measuring seismic velocity changes can sensitively probe changes in stress and damage, particularly in the shallow subsurface, but we need complementary methods to monitor deep crustal processes and to detect localized velocity changes. Receiver functions (RFs) provide a localized measurement of the crustal column and are uniformly sensitive to velocity changes throughout the crust. With over 1500 magnitude 5.0+ magnitude 5.0+ teleseismic earthquakes every year, RFs permit quasi-continuous monitoring of the crustal velocity structure.

We build a catalog of ~8,000 P-phase receiver functions for 12 stations near Ridgecrest using teleseismic events from 2015-2023. We use tools from optimal transport to disentangle independent modes of waveform variation in the RFs, isolating the signature of seismic velocity changes from changes in the backazimuth/slowness of the incident teleseismic waves. Using 1D velocity model inversions and perturbations to the resulting synthetic RFs, we localize the velocity perturbations at depth. We identify perturbations to a phase in the RF corresponding to a velocity change at ~15 km depth that changes sharply coseismically, decays over ~1 year, and persists with a static offset to the present-day. We discuss the extent and decay of the deep velocity changes in the context of the rupture at depth.

Bryan, J. T., Frank, W. B., & Audet, P. (2023, 09). Deep seismic velocity changes following the 2019 Ridgecrest earthquake. Poster Presentation at 2023 SCEC Annual Meeting.

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