Coseismic Rupture Process of the Large 2019 Ridgecrest Earthquakes From Joint Inversion of Geodetic and Seismological Observations

Abstract

On 4 and 6 July 2019, two large strike‐slip earthquakes with W‐phase moment magnitudes MWW 6.5 (foreshock) and MWW 7.1 (mainshock) struck the Eastern California Shear Zone, northeast of Ridgecrest. The faulting geometry and kinematic coseismic slip distribution of both events are determined by jointly inverting seismological and geodetic observations guided by aftershock and surface rupture locations. The foreshock ruptured two orthogonal faults with a prominent L‐shaped geometry with maximum slip of ~1.1 m on the NE‐SW segment. The mainshock faulting extended NW‐SE along several primary fault segments that straddle the foreshock slip. The surface rupture and slip model indicate mostly near‐horizontal strike‐slip motion with maximum slip of ~3.7 m, but there is a localized vertical dip‐slip motion. Both the foreshock and mainshock ruptures terminate in regions of complex surface offsets. High aftershock productivity and low rupture velocity may be the result of rupture of a relatively immature fault system.

Orthogonal Fault Rupture and Rapid Postseismic Deformation Following 2019 Ridgecrest, California, Earthquake Sequence Revealed From Geodetic Observations

“…A slip model with a zero dip-slip constraint in that zone has a significant residual around FS4 and FS7 at a level of 0.1 m ( Figure S10), which we deem unaccepted for the inversion in this study. As other seismic slip solutions (Liu et al, 2019) do not show the pattern, we suggest that this patch of slip could have mainly occurred aseismically after the mainshock. Note that an uncertainty map made in this study shows that the resolution of the data on the dip-slip component at depth of F7 is relatively weak ( Figure S10).…”

“…Knowledge about forthcoming earthquakes can improve preparedness if any signs pointing to the occurrence of a second event were captured immediately after the first one. In the studied earthquake sequence, there was a strong correlation between aftershocks following the Mw6.4 earthquake and the later Mw7.1 mainshock in space and time, a fact that has been noted in several studies (Barnhart et al, 2019;Liu et al, 2019;Melgar et al, 2019;Ross et al, 2019). However, to fully reveal the connection between the foreshocks and Mw7.1 mainshock, a detailed fault slip model is required, which is addressed in this study.…”

Stress Changes on the Garlock fault during and after the 2019 Ridgecrest Earthquake Sequence

“…The kinematic slip inversion we present resolves two primary slip patches (i.e., Fig. 1), which have similar amplitudes (4.7 and 2.5 m) and locations (northwest and southeast of hypocenter) to the Barnhart et al (2019), Liu et al (2019), and Zhang et al…”

Rapid Characterization of the July 2019 Ridgecrest, California, Earthquake Sequence From Raw Seismic Data Using Machine‐Learning Phase Picker

“…It was followed by an intense aftershock sequence leading up to the occurrence of the second mainshock, M W 7.1 at 03:19 UTC on 6 July 2019. The M W 6.4 and 7.1 mainshocks occurred closely in space (10-km separation) and activated a complex fault network composed of conjugate strike-slip faults including the NW-trending main fault with about 65-km-long surface rupture and NE-treading fault with~15-km-long surface rupture (Barnhart et al, 2019;Goldberg et al, 2019;Kendrick et al, 2019;Liu et al, 2019;Ross et al, 2019; Figure 1). A high-precision near real-time catalog enables us to rapidly characterize the earthquake sequence (Stewart, 1977), such as tracking seismicity evolution (Peng & Zhao, 2009;Ross et al, 2017;Zhang & Wen, 2015a) and identification of causative faults (Kao & Shan, 2007;Yang et al, 2009).…”