Mid-crustal controls on episodic stress-field rotation around major reverse, normal and strike-slip faults

Abstract

Abstract Numerical models are used to investigate the geometry of coseismic stress-field perturbation in the crust surrounding a reverse fault, a normal fault and a strike-slip fault. The results predict a coseismic stress drop in the upper crust and loading to high stress below the brittle–ductile transition (BDT) due to the taper-off in fault slip. Coseismic stress deflections occur for each fault type as a result of the coseismic stress redistribution and is at a maximum in the middle crust where fault slip tapers-off. The zone of high-stress deflection extends downwards to the base of the crust. During the post-seismic interval, the stress-field geometry recovers towards the pre-earthquake stress state, but simple stress-field geometries cannot be re-established. The numerical results indicate that: (1) stress deflection due to slip taper-off below the BDT is important for the stress perturbation throughout the crust; (2) predictions for coseismic stress deflection exclusively based on the fault-parallel shear-stress drop ratio systematically underestimate stress deflection in the entire crust; (3) stress rotation is persistent throughout the crust in seismically active regions; and (4) the geometry of secondary faults is expected to be affected by the perturbed stress field.