Dynamic asymmetry of normal and reverse faults due to constrained depth-dependent stress accumulation

Abstract

This paper reports asymmetric features of normal and reverse faulting from the point of view of earthquake dynamics. It is assumed that the fault's strength is governed by Coulomb friction, namely depending on normal stress, and numerical simulations are carried out using a boundary domain method, a hybrid coupling between the boundary integral equation and finite difference methods. Under the same uniform initial stress loaded on a fault, simulations reveal that stress perturbations from the ground surface accelerate rupture of a reverse fault but decelerate that of a normal fault when approaching the ground surface. Furthermore, the overburden stress increases with depth. A Mohr-Coulomb diagram constrains the possible stress accumulation, as the Mohr-circle should not exceed the static Coulomb friction. In such case, shear stress can be loaded sufficiently on reverse fault at any depth, while the stress accumulation is limited at a shallow depth of a normal fault. This difference leads to further favouring of reverse faulting at shallow depths and makes normal faulting difficult near the ground surface. The results suggest the importance of the initial stress conditions and dynamic stress perturbation for understanding earthquakemechanics and assessing potential earthquake scenarios in seismic hazard studies.