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SCEC2021 Plenary Talk, Fault and Rupture Mechanics (FARM)

Investigating the Influence of Topography on Rupture Propagation along Fault Stepovers

Roby Douilly

Oral Presentation

2021 SCEC Annual Meeting, SCEC Contribution #11102
Complex fault systems are often located in regions with asymmetric topography, and these systems are very common in Southern California. As an example, the eastern portion of the left-lateral Garlock fault system, which is composed of two segments separated by an extensional stepover width of 3-4 km, has high mountain ranges on its northern side and almost a flat topography on the southern side. The recent 2019 Ridgecrest sequence triggered significant seismicity on the Garlock fault particularly close the ruptured area and thus a potential rupture on the Garlock fault could either stop or propagate through this stepover. Previous rupture dynamic studies have investigated the effect of stepover widths on throughgoing rupture. However all these stepover studies assumed a flat topography and didn’t examine the impact of topography on the rupture behavior. Therefore in this study, to investigate the effect of topography, we consider three cases: a flat topography, a positive (mountain) and a negative (basin) topography on only one side of the fault system outside of the stepover, consistent with the configuration of the Garlock fault. In each case, we consider a suite of geometries with two 30 km long vertical planar segments with 5 km overlap and stepover widths of 1 to 7 km. We create a three-dimensional finite element mesh for each of those geometries and use FaultMod to compute the rupture dynamics. Similar to the results of Kyriakopoulos et al., 2018 who investigated the effect of asymmetric topography on rupture across a single fault, for ruptures initiated on the fault segment right next to the mountain or basin, our results show a significant time dependent variation of the normal stress for the topography cases as opposed to the flat surface case. Furthermore, a positive topography causes a clamping effect behind the rupture front, which leads to less slip on the fault, and the rupture is not able to jump as wide a stepover as in the flat topography case. The opposite is observed for the negative topography, where the rupture can jump over a wider stepover than the flat case. These results suggest that topography seems to have significant impact on throughgoing rupture and should be considered in dynamic studies with geometric complexities such as stepovers, bends and branch fault systems.