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

We use the 2D finite element method to determine how geometrical parameters determine whether rupture will propagate across a linked stepover in a strike-slip fault. The end segments of the fault system are aligned in the direction of maximum shear, and the length and angle of the linking segment are allowed to vary. 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; 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 case in which the end segments are aligned with the direction of maximum shear and the case in which the end segments are optimally oriented for rupture, the angles at which rupture could no longer propagate through the entire fault corresponded with peaks in the fault's S value.