Investigation on the jump distance of the strike-slip step overs based on the 3D dynamic rupture simulations

Abstract:

We constructed 3D strike-slip step over models in a homogenous half-space, and performed huge amounts of dynamic rupture simulations on the step overs. It is the first time to give dynamic rupture supports on a step over with step width larger than 10 km can be jumped under certain conditions, that is the strong inherent supershear rupture, free surface induced supershear rupture, zero cohesion and sufficiently long accelerating length of rupture fronts, occur on the main fault simultaneously. In the absence of the inherent supershear, the largest jump distance is 3.5 km, which supports the 3-4 km maximum jump distance observed in major field observations. Without the free surface induced supershear, the maximum jump distance for step overs decreases to 6 km, which is close to previous 2D numerical studies where no free surface effect is included. The existence of non-zero cohesion, though not large, can also significantly reduce the maximum jump distance. With a shorter accelerating length of rupture front on the main fault, rupture on step overs is probable to jump a lower step width. Results of the dynamic simulations show that the maximum jump distances for strike-slip step overs decrease as the dimensionless effective shear stress decreases, and all ruptures die on the main fault when the dimensionless effective shear stress decreases to 0.35. This work may help to explain the 10 km jump distance observed in the 2001 M7.8 Kunlun, China earthquake.