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Group A, Poster #129, Fault and Rupture Mechanics (FARM)

The role of sediments and fault damage on the 2019 Ridgecrest earthquake: a rupture impediment and/or ground motion amplifier?

Elif Oral, Jean-Paul Ampuero, & Domniki Asimaki
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #129, SCEC Contribution #11944 VIEW PDF
Observations of the 2019 M 7.1 Ridgecrest earthquake reveal a slow rupture (~ <= 2 km/s) and near-field ground motions with high spatial variability. The area is well characterized with sedimentary layers and low-velocity fault damage zones, but to what extent such local structure could affect the rupture is unknown. Also regarding ground motions, the interplay between a slow rupture, sedimentary layers, and damage is unclear, as they might play contrasting roles. Our objective is to elucidate the role of local structure on rupture and near field ground motion of the Ridgecrest earthquake. We model 3D dynamic rupture on a planar fault and use the recent 3D velocity model of White et al. (...2021), and damage zones of Qiu et al. (2021). We also consider past-seismicity-caused initial stress heterogeneity, using our recent method of Oral et al. (2022) and catalogued foreshocks. Our findings are: 1) Sedimentary layers with or without damage slightly affect the rupture speed, whereas a low background stress can be a sufficient factor to explain the observed slow rupture; 2) Sedimentary layers amplifies fault slip and consequent ground motion, counterbalancing the damping effect of a slower rupture; 3) A simple sub-shear bilateral rupture model well captures the observed ground motion directivity. We plan to expand our study on other areas in California with different fault zone properties, to identify whether the damage effect in Ridgecrest is a paradigm or unusual for the regional seismic hazard.