Rupture Scenarios in the Brawley Seismic Zone: Exploring the Dynamic Interactions Between the Southern San Andreas Fault and Normal Faults under the Salton Sea

The generation of large earthquakes along the Southern San Andreas fault (SSAF) depends on many rupture parameters that could aid or eventually terminate rupture propagation along the fault, and thus determine the severity of future events. Of particular importance is the initiation phase and subsequent triggering of the SSAF by adjacent smaller faults that could serve as both nucleation points and/or participate in larger multi-fault ruptures. A geographic area that could potentially host such types of interactions is the southern terminus of the SSAF, near Bombay Beach, CA. Southward from here the SSAF projects into the Salton Sea, and although it lacks a surface expression, it eventually steps over to the Imperial Fault (IF) with a transtensional step-over. The area that lies in between is known as the Brawley Seismic Zone (BSZ) and is characterized by continuous micro-seismicity and swarm-type activity. Although most of the seismicity in this area occurs along vertical left-lateral strike-slip cross faults that intersect the SSAF, there is clear evidence that displacement in the northern BSZ also occurs along normal faults (Brothers et al., 2009, Brothers et al., 2011) under the Salton Sea, which could also interact with the SSAF. For that reason, both the cross-faults and the normal faults in this area should be considered as candidate initiation structures for future large earthquakes. Here we extend our previous work regarding the dynamic interactions between the SSAF, the IF and the network of cross faults (Kyriakopoulos et al., 2019) to include the possible interaction between the SSAF and a normal fault under the Salton Sea. Toward this goal, we have designed a series of dynamic rupture scenarios that help us investigate how SSAF events can transfer slip onto the normal faults, and the mechanisms by which normal fault earthquakes could trigger a major event on the SSAF. Preliminary results indicate that in the case of earthquake ruptures initiating on the SSAF, the nucleation location (rupture approaching the fault intersection from the south or north) plays a determining role in the triggering of slip on the normal fault.