The Cajon pass earthquake gate: clues from synthetic and realistic topography dynamic rupture models

Christodoulos Kyriakopoulos, Baoning Wu, & David D. Oglesby

Submitted August 15, 2020, SCEC Contribution #10758, 2020 SCEC Annual Meeting Poster #163

The Cajon Pass (CP) is a key area for the generation of large earthquakes in southern California and is thought to be an “Earthquake Gate” (EG). EG’s are locations of structural complexity along major faults that, depending on a series of mechanical conditions, have the potential either to allow or stop the propagation of earthquake rupture. The mechanisms for which the CP serves as an EG are net yet understood, and for that reason are the focus of a SCEC5 interdisciplinary investigative effort. From this perspective , it is of great importance to identify first-order effects that modulate and control the generation of region-wide ruptures. Here we investigate whether the asymmetric disposition of the topographic features surrounding the CP could have an effect on this “gate-like” behavior. We organize our work to include three different types of dynamic rupture simulations. Models with a realistic (DEM based) topographic relief, models with flat free surface, and models with a synthetic topography (increasing ramp). Our experiments are further subdivided based on parameters such as nucleation location, locking depth and prestress conditions. In our preliminary results we observe a distinct pattern of normal stress change (not observed in the flat models) around the rupture front near the free surface. More specifically, in models with nucleation south of the CP (here the topography lies to the north of the fault), the rupture front is preceded by an increase in normal stress and followed by a concentration of decreasing normal stress. When rupture passes the CP (now topography lies to the south of the fault) the normal stress pattern is inverted. The same pattern of inversion is observed when rupture nucleates to the north of the CP and propagates southward. These preliminary results show that the CP marks a transition for rupture behavior and that this transition is (at least partially) related to the asymmetric disposition of the topographic relief.

Key Words
topography, dynamic rupture models, normal stress, earthquake gate, Cajon pass

Citation
Kyriakopoulos, C., Wu, B., & Oglesby, D. D. (2020, 08). The Cajon pass earthquake gate: clues from synthetic and realistic topography dynamic rupture models . Poster Presentation at 2020 SCEC Annual Meeting.


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