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Geometrical Fault Complexity and the Rupture Dynamics of the 2019 M6.4 and M7.1 Ridgecrest, California Earthquakes

Session: Exploring Rupture Dynamics and Seismic Wave Propagation Along Complex Fault Systems I

Type: Oral

Date: 4/19/2021

Presentation Time: 09:45 AM Pacific

Description: 

The largest earthquakes of the 2019 Ridgecrest, California earthquake sequence were a M6.4 earthquake on the morning of July 4^th, followed 34 hours later by a M7.1 on the evening of July 5^th. The primary fault for the M6.4 was a NE-striking left-lateral strike-slip fault, while the primary M7.1 rupture occurred on a NW-striking right-lateral strike-slip fault. However, many smaller NE-striking and NW-striking fault strands activated in one or both Ridgecrest mainshocks. Here, we use 3D dynamic rupture modeling to simulate the interactions between high-slip primary rupture traces in the Ridgecrest M6.4 and M7.1 earthquakes, as well as to investigate the roles of secondary lower-slip fault strands. We find that a model with one left-lateral fault for the M6.4 and one right-lateral fault for the M7.1 is able to produce a good first-order match for the magnitude and ground surface slip distributions for both events. In this model, dynamic clamping and shear stress reduction from the M6.4 rupture onto the future M7.1 fault plane confined surface rupture in the M6.4 to the left-lateral fault. We also run simulations on a more complex multi-strand fault geometry, to determine the role of these additional faults in the rupture dynamics and resulting slip distribution of the M6.4 and M7.1 Ridgecrest earthquakes. In particular, we investigate whether any right-lateral fault strands were involved in the M6.4, and whether surface expression of slip on smaller fault strands is due to their hosting dynamic rupture and producing significant moment release, or due to more passive effects such as triggered slip.

Presenting Author: Julian Lozos

Student Presenter: No

Authors