Dynamic rupture and cross-fault activation: the effect of high pre-stress contrast

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

Published August 15, 2018, SCEC Contribution #8784, 2018 SCEC Annual Meeting Poster #206

The Brawley Seismic Zone (BSZ) is postulated to consist of several cross-faults that are roughly perpendicular to the main fault structures in the area, including the Southern San Andreas (SSAF) and Imperial (IF) fault systems. This geometric configuration provides a natural laboratory to test potential dynamic interactions between cross-faults and adjacent main structures. In particular, we are interested in whether rupture of the main fault segments facilitates rupture of the cross-faults, and vice versa. We run 3D dynamic rupture models of the above system in the BSZ. Under constant traction assumptions, the perpendicularity of the cross faults to the SSAF and IF somewhat limits the dynamic interaction between them, and tends to hinder propagation of rupture from the main structures to the cross-faults. This is true whether the initial shear stress is low or high on the entire system. However, we find out that such interaction is more likely when there is a pre-stress contrast between the SSAF-IF system and the CFs, with the cross-faults pre-stressed at a significantly higher shear stress level than the main segments. This arrangement is plausible because the cross faults are more favorably oriented with the regional stress. With higher slip tendency, they should be closer to a critical stress threshold compared to the SSAF and IF structures. Importantly, it is the contrast in stress that facilitates such cross-fault rupture, not the absolute stress level. Furthermore, activation of the cross-faults can have a significant effect on rupture propagation on the main structures: slip on the cross faults can dynamically clamp one of the main structures, hindering rupture on it. An additional result is that if one of the main structures (the SSAF or IF) is constrained against slipping, rupture of the cross-faults is also facilitated, regardless of stress level. The resulting complex faulting patterns are reminiscent of other geometrically complex earthquakes, such as the Mw7.8 2016 Kaikoura, NZ event.

Key Words
dynamic rupture, San Andreas Fault, Imperial Fault, Cross Faults

Citation
Oglesby, D. D., Kyriakopoulos, C., Rockwell, T. K., Meltzner, A. J., Barall, M., & Fletcher, J. (2018, 08). Dynamic rupture and cross-fault activation: the effect of high pre-stress contrast. Poster Presentation at 2018 SCEC Annual Meeting.

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