Rupture propagation characteristics on a bending fault: Insights from numerical simulations of dynamic stress field

We investigate the propagation of spontaneous rupture on bending faults by numerical simulations based on the boundary integral equation method with unstructured meshes. Our results show that for a uniform initial stress field, the bending angle determines the initial stress state on the bending plane, which in turn affects the rupture propagation. In addition, the bending angle also constrains the dynamic stress field during in-plane ruptures, which controls the rupture velocity and detailed slip distribution near the bend. There are different rupture propagation behaviors on faults with restraining and releasing bends. For a restraining bend, rupture either terminates at the bend or pauses briefly and accelerates after crossing the bend. For large bending angles (60^o), rupture cannot continue to propagate onto the bending plane where the Coulomb stress decreases. For a releasing bend, the rupture on the bending plane propagates with much lower energy as the bending angle increases. Stress response function analysis indicates that the dynamic stress field near the rupture tip plays an important role in the rupture pattern on the bending plane, with positive and negative normal stress accumulations for restraining and releasing bends, respectively. The effect of the dynamic stress field on the rupture propagation on bending faults is similar to that by a barrier or asperity. However, for anti-plane shear ruptures, the dynamic normal stress field at the rupture tip is independent of the bending angle, and the rupture is dominated by the initial stress state.