Subsurface Damage Zones of the Sinistral Faults at Ridgecrest in the Eastern California Shear Zone Characterized by Fault-Zone Trapped Waves

Yong-Gang Li, Rufus D. Catchings, & Mark R. Goldman

Submitted August 16, 2021, SCEC Contribution #11591, 2021 SCEC Annual Meeting Poster #168

We use fault-zone trapped waves (FZTWs) to characterize damage zones of the multiple immature sinistral faults in the Eastern California Shear Zone (ECSZ) associated with the 2019 M6.4 and M7.1 Ridgecrest earthquake sequence. In the ECSZ, a cascading rupture occurred on multiple faults that connect at depth, rather than a single continuous rupture zone. We identified aftershock-generated FZTWs in seismograms recorded by dense seismic arrays deployed across surface ruptures shortly following the 5 July 2019 M7.1 mainshock. Observations and 3-D FD simulations of these FZTWs reveal low-velocity waveguides (LVWs) resulting from severely damaged fault rocks associated with the Ridgecrest earthquakes. These LVWs are characterized by segmentation, branching, and merging, consistent with surface ruptures. We observed and modeled a 1-2-km-wide zone, including several 300-500-m-wide waveguides along the ruptured faults with seismic velocities 30-50% lower than wall-rock velocities and greater velocity reduction (rock damage) at the shallower depths. The Ridgecrest LVWs along the Eastern Little Lake Fault (ELLF) likely extend to 5-7 km depth between the M7.1 and M6.4 epicenters and become shallower than 3-4 km northward and southward along the ~50-km-long rupture zone. We note that the velocity reductions and waveguide depths along the ELLF ruptured during the 2019 M7.1 Ridgecrest earthquake are similar to those along the faults ruptured during the 1992 M7.3 Landers earthquake in the southern ECSZ at Mojave Desert. Both continuous and widely distributed rupture zones may pose significant regional hazards from amplification and extended ground shaking along fault waveguides.

Citation
Li, Y., Catchings, R. D., & Goldman, M. R. (2021, 08). Subsurface Damage Zones of the Sinistral Faults at Ridgecrest in the Eastern California Shear Zone Characterized by Fault-Zone Trapped Waves. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)