SCEC Award Number 15161 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Modeling Rupture through the Brawley Seismic Zone Stepover: Can Ruptures Propagate between the San Andreas and Imperial Faults?
Investigator(s)
Name Organization
Thomas Rockwell San Diego State University David Oglesby University of California, Riverside Aron Meltzner Nanyang Technological University (Singapore)
Other Participants 1 SCEC intern to be named and Christodoulos Kyriakopoulos (post-doc)
SCEC Priorities 4e, 4a, 3e SCEC Groups FARM, SoSAFE, Geology
Report Due Date 03/15/2016 Date Report Submitted 03/08/2016
Project Abstract
 Paleoseismic observations indicate that the southern San Andreas and Imperial faults (SAF and IF) ruptured at similar times in past earthquakes, suggesting that they may have ruptured together during single events. Modeling of dynamic rupture scenarios that involve the southern SAF and IF suggests that large earthquakes may rupture through this large step-over, depending on rupture directivity and the presence of connecting faults or cross-faults, supporting the paleoseismic observations. Nucleation on the SAF favors rupture of both the SAF and IF in the step-over region, whereas nucleation on the IF ruptures primarily the western (IF) strand of the step-over. We interpret this asymmetry to reflect the geometrical complexity of the system, which leads to dynamic clamping and unclamping of the system at different locations and at different times.
Intellectual Merit Understanding whether large step-overs between major fault strands will always terminate large earthquake ruptures, or whether certain structural configurations may allow for slip to pass through these complexities is a key question in understanding large earthquake production on California’s system of plate boundary faults. UCERF3 assumes that ruptures can jump steps as much as 5 km in dimension, but some structural configurations may allow for larger jumps. This study models the southern San Andreas-Imperial fault step through the Brawley Seismic Zone to determine whether some structural configurations may allow ruptures to pass through and continue from one fault to the other.
Broader Impacts A great earthquake on the southern San Andreas fault, with surface rupture from Parkfield to the Salton Sea, will cut most major lifelines into southern California, including highways and major water conduits. One major highway that has been considered safe in such an event is the I-8 corridor, as it runs south of the southern terminus of the San Andreas fault. In this study, we consider whether it may be possible that a large earthquake can rupture through the large releasing step that comprises the Brawley Seismic Zone and produce rupture on the Imperial fault. Part of the impetus for this study is the recognition that some large earthquakes on the Imperial and southern San Andreas fault are indistinguishable in timing and could represent large earthquakes that ruptured both fault segments. If so, then all major highways and byways into southern California could be cut by such an event. Also, an undergraduate summer intern, Drew Tulanowski, was trained in producing 3D finite element meshes of the fault systems for the modeling effort, and participated in this research, and post-doc Christos Kyriakopoulos acted as a primary supervisor for Mr. Tulanowski, providing him with experience in training students.
Exemplary Figure Snapshots of rupture propagation on a 3D fault system with cross faults, modeled after the configuration of the southern San Andreas and Imperial faults. Cross‐faults are modeled from the well‐defined seismicity lineaments in the Brawley Seismic Zone.
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