Seismotectonics and Fault Geometries of the 2019 Ridgecrest Sequence: Insight From Aftershock Moment Tensor Catalog Using 3-D Green's Functions

Abstract

The 2019 M_w 7.1 Ridgecrest earthquake occurred on 6 July, preceded by the M_w 6.4 foreshock on 4 July 2019. These two earthquakes occurred close in space and time with partially overlapping surface ruptures and aftershock patterns, raising the question of the relationship between the two events. Geological surveys and satellite observations provide important constraints on the surface traces of faulting. However, the subsurface fault geometries, which are important for understanding the regional stress field, earthquake initiation, propagation, and termination, are not well resolved. In this study, moment tensor solutions for 256 earthquakes in the 2019 Ridgecrest sequence were determined by waveform inversion using 3‐D velocity model. The obtained moment tensor solutions show rotations of the stresses after mainshock, indicating the ratio of mainshock stress drop to the background stress to be 0.5–0.9. The obtained moment tensor catalog also facilitates a better understanding of the subsurface fault geometries, including (1) splay faults and antithetic faults in the northwest aftershock zone; (2) shallow flower structures near the M_w 7.1 epicenter; and (3) subparallel faults in the southeast aftershock zone. The aftershocks' studies suggest the very complex surface ruptures near the 2019 Ridgecrest M_w 7.1 epicenter are near‐surface features that linked to a simple large throughgoing fault at >5 km depth. We also found that the southeastern‐most aftershocks, which are located less than a kilometer from the Garlock fault trace, have significant different strike directions from that of the Garlock fault, indicating the central Garlock fault remains seismically quiet.