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Using Dynamic Rupture Simulations to Explore Fault Segmentation and Rupture Length on the Sierra Madre Fault Zone

Description: 

The Sierra Madre Fault Zone (SMFZ) is a 125 km-long, north to northeast-dipping thrust fault which arcs along the southern edge of the San Gabriel and Santa Susana Mountains in Los Angeles and San Bernardino counties, southern California. Based on its length alone, it is capable of producing a ~M7.7 earthquake, but its discontinuous geometry may lead to it rupturing in multiple smaller (~M6-M7) events (such as the M6.6 1971 San Fernando earthquake). Given the SMFZ’s location through the densely-populated San Fernando, San Gabriel, and San Bernardino valleys, even a smaller event on this fault would have major implications for human safety and infrastructure stability.

We conducted 3D dynamic rupture simulations on the SMFZ, which we parameterize with four separate segments, to assess plausible rupture behaviors and ground motion distributions for this fault system. We use Southern California Earthquake Center (SCEC) Community Fault Model geometry, SCEC Community Velocity Model surrounding rheology, and SCEC Community Stress Model regional stress orientations to ensure that our model setup is grounded in observation and that our results are realistic. We find that the segmented, nonplanar geometry of the SMFZ controls its possible rupture behaviors, with the nucleating segment playing the largest role. Ruptures that nucleate on the ends of the fault system are limited by stepovers, and do not allow more than a small amount of slip beyond the nucleating segment. Ruptures that nucleate in the center of the system propagate through at least two segments, and sometimes may grow into a wall-to-wall rupture of the whole fault system; this also depends strongly on nucleation location. The maximum magnitude of our simulations is M7.47; there are several different slip distributions for this magnitude, however, which produce different ground motion distributions and intensities. This suggests that the details of slip distribution and rupture directivity are critical for ground motion intensity estimates, both on the SMFZ and in general.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia

Type: Oral

Date: 4/20/2023

Presentation Time: 05:15 PM (local time)

Presenting Author: Julian Lozos

Student Presenter: No

Invited Presentation: 

Authors