Group , Poster #125, Fault and Rupture Mechanics (FARM)

Investigating the Effects of Fault Dip Angle on Rupture Propagation Along Branch Fault Systems Using Dynamic Rupture Simulations

Evan O. Marschall, & Roby Douilly
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Poster Presentation

2021 SCEC Annual Meeting, Poster #125, SCEC Contribution #11105 VIEW PDF
An important consideration in assessing seismic hazards is determining what is likely to happen when an earthquake rupture encounters a geometric complexity such as a branch fault. Previous studies showed parameters such as branch angle, stress-orientation and stress heterogeneity as key factors in the self-determined rupture path on branch faults. However, most of these studies were conducted in 2-D space or in 3-D with perfectly vertical faults. Many natural strike slip faults do not form perfectly vertical and have some dipping angle. In this study, we investigate the effects of dipping angle on rupture propagation along branch faults. We construct 3-D finite element meshes with varying d...ip angles (90º,75º,55º) with a 40 km long main fault intersected by a 20 km branch fault at an angle of 50°. We discretize the model space using tetrahedral elements with a mesh size of 100 m on the fault planes. These meshes are implemented into the dynamic rupture code FaultMod to model the rupture process governed by a linear slip-weakening friction law with a range of stressing angles (angle the maximum horizontal principal stress makes with the main fault). As demonstrated by prior work, for vertical faults, rupture initiated on the main fault will remain on the main fault and bypass the branch fault for particular sets of stressing angle. However preliminary results, for the same stressing angle as for the vertical faults, show that only varying the dip angle of the branch fault is enough to facilitate a througoing rupture along both the main and branch faults. The shallower the dipping angle of the branch fault, the more likely it is for the rupture to propagate onto them. These results indicate that dip angle is an important parameter in determination of rupture path on branch fault systems, with potentially significant impact for seismic hazard and should be taken into account in future earthquake modelling.
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