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The Effects of Fault Bends on Rupture Propagation: A Geometrical Parameter Study

Julian C. Lozos, David D. Oglesby, Benchun Duan, & Steven G. Wesnousky

Submitted 2010, SCEC Contribution #1337

We use a 2D finite element method to model a segmented strike-slip fault in which two parallel segments are connected across a step to determine what geometrical parameters prevent rupture from propagating through the entire system. The end segments of the fault system are taken to be aligned in the direction of maximum shear and the length and angle of the linking segment are allowed to vary. We identify several rupture behaviors, including jumps in rupture from one fault segment to the next, as well as a stalled rupture front being restarted by a stopping phase wave reflected off the other edge of the fault. We observe that ruptures propagate through extensional stepovers with steeper angles and longer linking segments than otherwise equivalent compressional stepovers. These different rupture behaviors form distinct regions in angle-stepover-length parameter space; the boundary between these regions takes the shape of an asymptotic curve in both the extensional and compressional cases. Models in which the size of the entire fault system was made larger or smaller revealed that the location of the boundaries between regions of different rupture behavior do not scale linearly with the system size, and that it was easier to rupture steeper and relatively longer stepovers in fault systems that were larger overall. A separate set of models in which the stress field is rotated so that the parallel end segments were optimally aligned for rupture significantly altered the rupture behavior curves; in this stress field, it was easier to rupture compressional stepovers with steeper angles and longer linking segments than it was to rupture equivalent extensional stepovers. In both the basic case and the stress rotation case, the angles at which rupture could no longer propagate through the entire fault corresponded with peaks in the fault’s strength excess.

Lozos, J. C., Oglesby, D. D., Duan, B., & Wesnousky, S. G. (2010). The Effects of Fault Bends on Rupture Propagation: A Geometrical Parameter Study. Bulletin of the Seismological Society of America, (submitted).