SCEC Award Number 23105
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Role of inherited fault geometry and complex fault structures in promoting correlated ruptures across multiple faults
Name Organization
Christine Regalla Northern Arizona University
Other Participants Aubrey LaPlante, NAU graduate student
SCEC Priorities 5b, 5d SCEC Groups Geology, FARM, SDOT
Report Due Date 03/15/2024 Date Report Submitted No report submitted
Project Abstract
This study modeled different source-receiver fault parameters and Coulomb stress changes on receiver faults, which could lead to static triggering or coordinated earthquakes between faults within Panamint Valley and Searles Valley, in the northern Eastern California Shear Zone (ECSZ). This work was motivated by paleoseismic data that indicate overlap in the timing of late Holocene earthquakes on the Panamint Valley fault, Ash Hill fault, and the Panamint Valley transtensional relay (PVTR) suggesting that these faults can rupture in coordinated, triggered, or multi-fault events. We conducted Coulomb stress modeling, using Coulomb 3.3 where we varied earthquake-source fault locations, fault kinematics, and subsurface fault geometries, to produce Coulomb stress change maps. We find that all modeled geometries and slip distributions of the Panamint-Ash Hill-PVTR source-receiver fault system generally produced Coulomb stress changes that discourage earthquake triggering via static stress transfer. However, indicate that static stress transfer is possible between a Manly Pass-Searles Valley source fault system and the receiver faults of Panamint, Ash Hill and/or the PVTR. If the Panamint, Ash Hill, and PVTR faults do rupture in closely timed events, as is suggested by paleoseismic data, the results of this study imply that they are unlikely to be rupturing at similar times as a result of triggering by static stress transfer. Alternatively, dynamic triggering or multifault rupturing may be required to explain the observed overlap in earthquake timing in the Panamint Valley.
Intellectual Merit This project focused on testing a possible mechanism for multi-fault or triggered earthquakes in a portion of the Eastern California Shear Zone. Such phenomena have been documented elsewhere in the ECSZ for historical and paleoseismic earthquakes (Hauksson et al., 1993; Cramer and Darragh, 1994; Jones and Hough, 1995; Hauksson et al., 2002; Rymer et al., 2002; Fletcher et al., 2014; Yamashita et al., 2022; Vadman et al., 2023). Here we focused on testing the role of inherited low angle fault geometries on promoting static (coulomb) stress changes that could promote failure on adjacent fault systems. We find that, at least within the Panamint Valley, low and high angle fault geometries are not conducive to static stress transfer on adjacent systems such that this is an unlikely explanation for coordinated paleoseismic ruptures observed in the system.
Broader Impacts This project supported the training of a graduate research of a female PhD student, A. LaPlante, who used this project to learn about static stress changes caused by fault slip, and to investigate the possible 3D sub surface fault geometries of a complex system involving both inherited and new faults. The results of this research have implications for understanding the fault geometry and stress conditions that can promote multi fault or triggered earthquakes.
Exemplary Figure Figure 4: Modelled coulomb stress changes on a receiver fault with a strike and dip of 162°/80°, and a rake of -170. a) A Panamint fault source with high-angle geometry (Model A;CFM 5.3), b) a Panamint fault source with modified low angle geometry (Model B; Modified CFM 5.3), c) a Manly Pass-Searles Valley fault source with high angle Panamint fault geometry (Model A;CFM 5.3), and d) a Manly Pass-Searles Valley fault source with modified low-angle Panamint fault geometry (Model B;CFM 5.3). Figure Credit: Aubrey LaPlante.