Source Imaging With a Multi‐Array Local Back‐Projection and Its Application to the 2019Mw6.4 andMw7.1 Ridgecrest Earthquakes

Abstract

AbstractThis study aims to improve the multi‐array local back‐projection (MLBP) approach and to apply it to the 2019Mw6.4 andMw7.1 Ridgecrest, California earthquakes to resolve more details about their kinematic process, with the dense seismic network in California. Compared with teleseismic BPs, seismic array processing with stations located at local to regional distances images earthquake rupture process more quickly with higher resolution. To increase the objectivity of stations selection criteria and to be prepared for future real‐time BP implementations, we improve MLBP with an automatic procedure to group stations based on waveform coherence. We also apply empirical aftershock calibrations to account for the 3D path effect. Our MLBP highlights the rupture complexity in a multi‐fault system. TheMw6.4 quake initiates on a 5‐km‐long NW‐trending segment, then ruptures the primary SW‐trending fault at the speed of ∼1.3 km/s. TheMw7.1 quake ruptures bilaterally for 10 and 22 km, on the NW and SE portion of the fault, respectively, at the speed of 1–1.6 km/s. The rupture paths agree with aftershock distributions and surface rupture estimated from satellite imagery. The slow rupture propagation may be driven by the low structural maturity of the fault. This case study demonstrates the effectiveness of MLBP for earthquake source imaging and rapid hazard assessment.