SCEC Award Number 17055 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Can earthquake swarms trigger the San Andreas fault in the Brawley seismic zone? Continued study of dynamic rupture scenarios in the Salton Trough region.
Name Organization
Christodoulos Kyriakopoulos University of California, Riverside David Oglesby University of California, Riverside Thomas Rockwell San Diego State University Aron Meltzner Nanyang Technological University (Singapore)
Other Participants
SCEC Priorities 1d, 3a, 5b SCEC Groups FARM, SAFS, CS
Report Due Date 06/15/2018 Date Report Submitted 06/15/2018
Project Abstract
We have continued our investigation of multi-fault dynamic rupture scenarios in the Brawley Seismic Zone (BSZ). Our models are based on a postulated fault geometry that includes the extensions of the Southern San Andreas Fault (SSAF) and the Imperial Fault (IF), as well linking cross-faults (CF) intersecting the SSAF and IF. Our previous results have shown that, with our current fault geometry and under the current model assumptions, a through going rupture in this area is possible. However, many questions remained open regarding the influence of the CF in the overall rupture. In this work, we significantly extended the investigated parameter space to include new rupture scenarios that include a pre-stress contrast between the SSAF-IF and CF, segmented faults, nucleation location near the branch, nucleation on a cross-fault, shallower locking depth, and other features. The new experiments are based on a combination of modified fault geometries and different pre-stress conditions. Results from SCEC Award #17055 expanded significantly our understanding of the possible mechanism that could led to a multi fault event and highlighted the importance of dynamic rupture simulations. We were able to verify that if the system of CF is pre-stressed at a higher level than the SSAF-IF main faults (consistent with regional stressing), the CF could modulate the normal stress on the SSAF-IF and provide a mechanism for earthquake termination. We also explored the effect of a shallower locking depth and fault segmentation that proved to be a significant parameter for the propagation of rupture across the BSZ.

Intellectual Merit We extended our investigation of possible joint rupture scenarios of the SSAF-IF system and their dynamic behavior when intersected by a system of linking cross-faults. The new experiments include models with a) non-homogeneous initial tractions (pre-stress contrast) between the SSAF-IF and the CF; b) experiments with segmented versions of the SSAF-IF; c) experiments with shallower locking depth (15km); d) experiments with nucleation location near the branches; e) experiments with nucleation on a cross-fault.
Broader Impacts Although less studied, the southward extension of the SSAF raises many questions regarding a possible interaction with the IF. A possible scenario involving both these faults could be the one in which a rupture nucleating near Bombay Beach will propagate bilaterally to the north, through the Coachella valley, and to the south into the BSZ and eventually connect with the IF. Such event has the potential to disrupt and damage interstate I-8, considered to be a safe corridor in case of the “big one”. Nevertheless, for such a scenario to be possible the hypothetical rupture must travel through the BSZ and successfully overcome the combined effect of possible gaps between the SSAF and IF but also the effect of several cross-faults intersecting the SSAF-IF system. In other words, this type of scenario will probably require the activation of several faults. Our study attempts to throw some light in the dynamic behavior of this system. We conducted an extensive study of parameters we believe might play a role in the final outcome of such event.
Exemplary Figure The figure is the one in section "Exemplary Figure".