SCEC Award Number 16229 View PDF
Proposal Category Collaborative Proposal (Special Fault Study Area)
Proposal Title Dynamic models of earthquakes in the Eastern San Gorgonio Pass
Investigator(s)
Name Organization
David Oglesby University of California, Riverside Michele Cooke University of Massachusetts Amherst
Other Participants Roby Douilly, postdoctoral researcher
SCEC Priorities 4a, 4e, 3c SCEC Groups CS, SoSAFE, FARM
Report Due Date 03/15/2017 Date Report Submitted 06/05/2017
Project Abstract
 One of the most important seismological issues in Southern California is the maximum probable earthquake size along the San Andreas fault (SAF). Resolving this issue may hinge on understanding the rupture behavior in the eastern San Gorgonio Pass (SGP): in this region, the San Andreas fault system forms a restraining bend with two possible paths for earthquake rupture. The behavior of rupture through the SGP is of fundamental importance to the maximum earthquake size in Southern California, the rate of large to great earthquakes, ground motion, and seismic hazard. In 2016, we began performing 3D dynamic finite element models of potential earthquakes in the Eastern San Gorgonio Pass region to help assess likely rupture paths of earthquakes. We used the most accurate fault representations available, as well as fault stresses determined through constant-traction and regional stress assumptions. In addition, we have derived stress fields through long-term quasi-static modeling that are consistent with measured slip rates and uplift patterns in the region. The stress fields are estimated from the produce of stressing rates time since last event as was as effects of recent large earthquakes. We are close to implementing these stress in our dynamic models. The results will have important implications for earthquake occurrence in the SGP, as well as for seismic hazard throughout Southern California. This work dovetails very well with our own prior modeling efforts in the Western San Gorgonio Pass, as well as the broader work of the San Gorgonio Pass Special Fault Study Area (SFSA).
Intellectual Merit Our results may have important implications for seismic hazard in both the immediate San Gorgonio Pass region and wider Southern California. The current results imply that the northern route toward the San Gorgonio Pass may be more favorable for rupture than the southern routes that appear to connect through the San Gorgonio Pass thrust fault system. Thus, it may be very important to determine the degree of fault activity and connectivity for the northern strands, such as the Mission Creek and Mill Creek. This kind of work is a hot topic for the continued work of the SCEC community as part of the San Gorgonio Pass SFSA and beyond into SCEC5.
Broader Impacts This grant supported the career of a postdoctoral researcher at UCR from a historically under-represented background in science. His research on this project has helped him secure a faculty position at UC Riverside. It has also supported the work of a female graduate student at UMass-Amherst. The work will have implications for estimation of seismic hazard and risk in Southern California.
Exemplary Figure
Figure 6. Dynamic modeling results for constant traction cases. High-normal-stress models are on top, and low-normal-stress models are on bottom; SCEC CFM v. 4,0 fault geometry is on left, and CFM v3 fault geometry is on right. The results differ for different stress assumptions and different geometries.
Linked Publications

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