Multi-fault models of the 2019 Ridgecrest sequence highlight complementary slip and fault junction instability

Abstract:

The 2019 Ridgecrest Mw 6.4 and Mw 7.1 earthquakes ruptured a complex fault system, posing challenges in understanding their physical processes. Modeling of the ruptures relies on fault geometries at depth, which are usually assumed based on surface traces and aftershocks. Here we use a variety of data including near and far field seismic data, high-rate GPS time series and Interferometric Synthetic Aperture Radar data to jointly constrain the fault geometries and slip distributions, using 3D Green’s functions to avoid potential bias from the complicated near-source geology. We first represent the first-order rupture processes with a series of subevents, then conduct slip inversions with subevent-guided fault geometries. We find that the foreshock sequentially ruptured the NW- and SW-trending faults starting from their junction. The mainshock initiated at a complex three-fault junction along the extension of the foreshock NW rupture, with major slip first occurring bilaterally near the hypocenter and then minor unilateral slip later to the southeast end. The slip distributions of the foreshock and mainshock are complementary to each other on the overlapping fault section.