Can the Southern San Andreas Fault be Triggered by Cross-Fault Earthquakes?

Christodoulos Kyriakopoulos, David D. Oglesby, Aron J. Meltzner, Thomas K. Rockwell, & Michael Barall

Submitted August 15, 2017, SCEC Contribution #7795, 2017 SCEC Annual Meeting Poster #177

The Brawley Seismic Zone (BSZ) is the step-over region between what is believed to be the southern terminus of the southern San Andreas Fault (SSAF), near Bombay Beach, and the northern end of the Imperial Fault. Within the past 30 years, numerous seismic swarms and small to medium size earthquakes have occurred in this region (Hauksson et al., 2013, Hauksson et al., 2017). Lineaments of seismicity within the BSZ clearly highlight several NE-SW oriented cross-fault structures. The cross-faults are the only recognizable faults in this area and are left-lateral to accommodate the regional right-lateral shear. Although no surface trace has been found south of Bombay Beach, it is reasonable to expect that the SSAF extends south of Bombay beach and is probably intercepted by one or multiple cross-faults. This implies a possibility for interaction between the SSAF and the cross faults. Support for this notion is provided by the 1987 Superstition Hills sequence (Magistrale et al., 1989). In this case the main Ms 6.6 strike-slip right-lateral event was promoted (unclamping) by slip on a left lateral cross fault (Ms6.2) intercepting the main fault (Hudnut et al., 1989) and occurred 11h earlier. Could this be also a triggering mechanism for a major SSAF event? To investigate this question, we use dynamic rupture models of earthquakes nucleating on a cross-fault. The size of the earthquake is varied from ~M5 up to M6 by progressively increasing the allowed area of rupture. We also investigate the effects of proximity of the nucleation to the SSAF from the actual earthquake size. We consider two different nucleation scenarios. In the first, we fix the hypocenter and allow the rupture to grow to the edges of the cross fault. In the second, we fix the edge of the rupture to be adjacent to the SSAF, and we allow the hypocenter to move outward as the rupture size increases. Our experiments will help us verify conditions under which a rupture could propagate from a cross-fault onto the SSAF.

Citation
Kyriakopoulos, C., Oglesby, D. D., Meltzner, A. J., Rockwell, T. K., & Barall, M. (2017, 08). Can the Southern San Andreas Fault be Triggered by Cross-Fault Earthquakes?. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)