Complex Rupture of an Immature Fault Zone: A Simultaneous Kinematic Model of the 2019 Ridgecrest, CA Earthquakes

Abstract

The 4 July 2019 Mw6.4 and subsequent 6 July 2019 Mw7.1 Ridgecrest sequence earthquakes (CA, USA) ruptured orthogonal fault planes in a low slip rate (1 mm/year) dextral fault zone in the area linking the Eastern California Shear Zone and Walker Lane. This region accommodates nearly one fourth of plate boundary motion and has been proposed to be an incipient transform fault system that could eventually become the main tectonic boundary, replacing the San Andreas Fault. We investigate the rupture process of these events using a novel simultaneous kinematic slip method with joint inversion of high‐rate GNSS, strong motion, GNSS static offset, and Interferometric Synthetic Aperture Radar data. We model the Coulomb stress change to evaluate how the Mw6.4 earthquake may have affected the subsequent Mw7.1 event. Our findings suggest complex interactions between several fault structures, including dynamic and static triggering, and provide important context for regional seismic source characterization and hazard models.

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

“…5c). In contrast, the northwest rupture front propagates at a more uniform speed (∼2:1 km=s) before decelerating and stopping at ∼25 s. These rupture speeds are consistent with recent kinematic models that prescribe a constant sub-Rayleigh mainshock rupture speed (Liu et al, 2019;Ross et al, 2019;Goldberg et al, 2020;Zhang et al, 2020). Rupture speed depends on how much total available energy is partitioned into radiated or fracture energy during the faulting process.…”

“…Barnhart et al (2019) observed that an increase in the Coulomb stress change (ΔCFS) from the Ridgecrest earthquake was correlated with the surface deformation after the earthquake. Studies have also suggested that the M w 6.4 foreshock and other large foreshocks promoted the rupture of the mainshock (Barnhart et al, 2019;Goldberg et al, 2020;Lozos and Harris, 2020).…”

“…We utilize seismic and GPS datasets to constrain the slip, which is similar to the approach by Liu et al (2019). In contrast, other studies make use of a combination of seismic, high-rate GPS and InSAR (Ross et al, 2019;Chen et al, 2020;Goldberg et al, 2020), InSAR and optimal image tracking (Barnhart et al, 2019), or only seismic datasets (Zhang et al, 2020). The details of slip distribution, and in particular the relative location and amplitude of maximum slip, varies between studies.…”

“…Several kinematic slip models have been developed to estimate the evolution of slip and rupture propagation during this highly complex sequence (Barnhart et al, 2019;Liu et al, 2019;Ross et al, 2019;Chen et al, 2020;Goldberg et al, 2020;Zhang et al, 2020). These models are consistent in the respect that a majority of foreshock and mainshock slip is limited to the upper 10 km depth.…”

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

“…A major difference in maximum slip amplitude occurs between our model and the Ross et al (2019) study, which estimates as much as 9 m of slip between 5 and 10 km depth. Other notable changes between our study and other's include a more widely distributed higher (>4 m) slip distribution , or a maximum slip amplitude difference on the order of 1.5 m between what is resolved from our inversion (4.7 m) and the Goldberg et al (2020) (∼3:5 m) study. Such differences are most likely due to the datasets used to constrain the inversions as well as the particular inversion parameterization.…”