SCEC Award Number 11140 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Correlation of peak dynamic and static Coulomb failure stress with seismicity rate change after the M7.2 El Mayor-Cucapah earthquake
Investigator(s)
Name Organization
Kim Olsen San Diego State University
Other Participants Graduate student, to be announced
SCEC Priorities A4, A6, A9 SCEC Groups EFP, Seismology, FARM
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 We have investigated the relation between the April 4 Mw7.2 El Mayor-Cucapah earthquake and seismicity rate changes in southern California and northern Baja California in the months following the mainshock. Specifically, we use a dynamic rupture model with observational constraints for the event simulated in the SCEC 3D CVM4.0 (Roten and Olsen, 2009) to calculate the changes in the resulting static (dCFS) and dynamic Coulomb failure stress, parameterized by its largest positive amplitude (peak dCFS(t)). We find that the correlation parameter is greater for peak dCFS(t) compared to dCFS, and highest for periods after the mainshock of longer than 1 week, and a peak at 1 month for both dCFS and peak dCFS(t). The stress changes are rotated onto the focal mechanism of the June 15, 2010 Mw5.7 aftershock as well as onto optimum oriented planes. For regionally rotated stresses we find that while the dCFS values are very similar for the two CVMs, the corresponding peak dCFS(t) values are noticeably different. In particular, CVM-H generates a lobe of (directivity-induced) large peak dCFS(t) between the Elsinore and San Jacinto Faults toward the Los Angeles basin not present in the results from CVM-4. However, both CVMs produce similar peak dCFS(t) lobes near San Diego. Finally, we searched for threshold levels of dCFS and peak dCFS(t) that may be required to trigger earthquakes of different magnitude that might provide clues to earthquake prediction; we found a possible peak dCFS(t) threshold value of 0.7 bars for aftershocks in regions of positive static stress.
Intellectual Merit The project addresses the problem of how earthquakes start, in particular triggered earthquakes/aftershocks. This is an important problem priority for SCEC, and we have approached the problem by comparing static and dynamic stress changes after the El Mayor Cucapah earthquake. We find a greater correlation between seismicity rate change after the mainshock and the dynamic stress changes.
Broader Impacts The study of the triggering potential of different parameters represents an important step toward understanding why earthquakes start. If a robust triggering parameter can be found, seismology has made a large step toward mitigating catastrophic results of earthquakes.
Exemplary Figure Figure 3. (left) Static and (right) peak dynamic stress changes (in bars) calculated from CVM-4, rotated onto a strike of 310 degrees, corresponding to the rupture of the Mw 5.72 June 15, 2010 event (epicenter depicted by the white star, mainshock by black star). Note how the dynamic stresses is in general agreement with the area of increased seismicity in southern California after the El Mayor-Cucapah earthquake. Credit: Kyle Withers.