SCEC2021 Plenary Talk, Fault and Rupture Mechanics (FARM)

Unraveling the mechanics of multi-fault earthquakes using realistic 3D dynamic rupture models, unifying interdisciplinary geophysical observations: the 2019 Ridgecrest sequence

Thomas Ulrich, Taufiq Taufiqurrahman, Alice-Agnes Gabriel, Duo Li, Bo Li, Sara Aniko Wirp, Sara Carena, Alessandro Verdecchia, & Frantisek Gallovic

Oral Presentation

2021 SCEC Annual Meeting, SCEC Contribution #11115
The July 4 and 5, 2019, Mw6.4 and Mw7.1 Ridgecrest, California events are prominent additions to a long series of multi-fault earthquakes (such as the 1992 Landers, 2010 Haiti, 2010 El Mayor‐Cucapah, 2016 Kaikoura events), which suggest that such complicated earthquakes may be more common than often assumed. To properly assess the associated seismic hazard, it is essential to analyze complex events carefully, in particular: to understand which conditions may promote their occurrence, to disentangle rupture sequences by carefully analyzing observables, and to analyze the associated strong motions, including identifying features specific to multi-fault events. Nevertheless, constraining the kinematics of multi-fault ruptures is challenging. Supercomputing empowered 3D dynamic rupture modeling, which provides physically self-consistent descriptions of how the complex fault network yields and slides, is now able to complement data inversion efforts towards better understanding the mechanical conditions driving cascading ruptures.

Here, we analyze the 2019 Ridgecrest sequence in the light of previous earthquakes we modeled, including the 1992 Landers, 2016 Kaikoura, and 2018 Palu earthquakes. We present a dynamic rupture scenario across a complex quasi-orthogonal fault system, assimilating community velocity and stress models, and long-term stress change analysis.
Our scenario unifies seismic, geodetic, and geological observations including fault surface offsets, shallow slip deficit, GPS and InSAR surface deformation, moment rate release, slip distribution, teleseismic, and strong ground motion waveforms in a physics-based manner. Our scenario of the Mw6.4 Searles Valley event ruptures two quasi-orthogonal faults while not triggering the Mw7.1 Ridgecrest event. Our scenario of the mainshock is able to break through the foreshock’s stress shadow while capturing important features, such as a crack-to-pulse transition and the re-rupturing of the main fault orthogonal segment. Our models offer new insight into how complex fault systems within the Eastern California Shear Zone may operate and allow designing more realistic scenarios of future earthquakes.