Poster #156, Fault and Rupture Mechanics (FARM)

Modeling the Rupture Dynamics of Strong Ground Acceleration (>1g) in Fault Stepovers

Holland Ladage, Julian C. Lozos, & Sinan O. Akciz
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Poster Presentation

2020 SCEC Annual Meeting, Poster #156, SCEC Contribution #10685
Following the July 2019 Ridgecrest earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their place in the desert pavement along the right-lateral strike-slip M7.1 rupture trace. This implies localized ground motions in excess of 1 g, in contrast to instrumentally recorded ground motions which peak at ~0.7 g. However, these features are not pervasive along the entire rupture; they are concentrated entirely within extensional stepover region near the southern end of the M7.1 rupture. Similar observations of displaced rocks concentrated in stepovers exist for the predominantly right-lateral strike-slip 2010 M7.2 El Mayor-Cucapah earthquake.... Together, the Ridgecrest and El Mayor-Cucapah examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration.

Here, we use the 3D finite element method to investigate how the geometry and connectivity of stepovers in strike-slip faults influences strong ground acceleration. In particular, we focus on how the amount of overlap between the two fault strands, and the width of the stepover, influences the location and intensity of the strongest ground motion, for both subshear and supershear rupture velocities.

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