The effect of depth-dependent stress on supershear rupture velocity transition on strike-slip faults

Abstract:

Earthquake rupture velocity, if greater than the shear wave speed, may facilitate the formation of a Mach front at the free surface, which in turn may propagate large amplitude ground motion to points on the surface at significant distance. The Earth’s free surface facilitates the generation of supershear ruptures in strike-slip faults, allowing such propagation at initial shear stress values lower than the value predicted for the Burridge-Andrews supershear transition mechanism. Recent work also shows that such free-surface-induced supershear rupture can be ephemeral, with the supershear daughter crack at the free surface sometimes slowing to sub-Rayleigh speed even in a homogeneous stress regime. Realistic depth-dependent stress plays a key role in the rupture velocity transition for the free-surface-induced supershear rupture. By performing dynamic rupture simulations with different depth-dependent stress regimes, we explore the influence of depth-dependent stress in controlling the rupture velocity transition in strike-slip faults, which may help in the interpretation of supershear rupture observations and in deducing initial stress condition from a given rupture velocity distribution.