Structural controls over the rupture and aftershocks of the 2019 Ridgecrest earthquake sequence investigated by high-fidelity elastic models of velocity structures

Sui Tung, Manoochehr Shirzaei, Chandrakanta Ojha, Antonio Pepe, & Zhen Liu

Under Review March 28, 2021, SCEC Contribution #10973

We develop finite element models of the coseismic displacement field accounting for the 3D elastic structures surrounding the epicentral area of the 2019 Ridgecrest earthquake sequence containing two major events of Mw7.1 and Mw6.4. The coseismic slip distribution is inferred from the surface displacement field recorded by Interferometric Synthetic Aperture Radar. The rupture dip geometry is further optimized using a novel nonlinear-crossover-linear inversion approach. It is found that the accounting for elastic heterogeneity and fault along-strike curvilinearity improves the fit to the observed displacement field and enhances the estimated geodetic moment and Coulomb stress changes. We observe spatial correlations among the locations of aftershocks and patches of high slip, and rock anomalous elastic properties, suggesting that the shallow crust's elastic structures possibly controlled the Ridgecrest earthquake sequence. Most of the coseismic slip with a peak slip of 7.4 m at 3.6 km depth occurred above a zone of reduced S-wave velocity, and significant post-Mw7.1 afterslip. This implies that viscous materials or fluid presence might have contributed to the low rupture velocity. Moreover, the zone of high slip on the northwest-trending fault segment is laterally bounded by two aftershock clusters, whose location is characterized with intermediate rock rigidity. Notably, some minor orthogonal faults consistently end above a subsurface rigid body. Overall, these observations of structural controls improve our understandings of the seismogenesis within incipient fault systems.

Citation
Tung, S., Shirzaei, M., Ojha, C., Pepe, A., & Liu, Z. (2021). Structural controls over the rupture and aftershocks of the 2019 Ridgecrest earthquake sequence investigated by high-fidelity elastic models of velocity structures. JGR, (under review).