Unexpected rupture triggering behavior of subshear and free-surface-induced supershear ruptures on stepover

The ability of a rupture to propagate across a stepover plays a critical role in determining the earthquake’s final magnitude and potential damage. This study systematically investigated the jump distances of 3D strike-slip faults based on the rate- and state-dependent friction law with strong rate weakening. Moreover, we compared the rupture triggering behavior of subshear and free-surface-induced (FSI) supershear ruptures on the secondary fault. Unexpectedly, both simple and barrier models have demonstrated that, compared to FSI supershear rupture, subshear rupture can result in a larger jump distance for the compressional step due to its stronger dynamic stress perturbation. The free surface also plays an important role in this process. Subshear rupture also shows a stronger triggering ability for the extensional step in models that consider the rate-strengthening layer and depth-dependent stresses, as well as models with different overlap distances. These results emphasize the high cascading rupture potential of subshear ruptures and provide important insights for assessing seismic hazards of multi-fault systems.