Numerical Simulations of Earthquake Triggering by Dynamic and Static Stress Changes Based on a Revised Friction Law

Abstract

We conducted numerical simulations of earthquake triggering by assuming a circular asperity using a rate- and state-dependent friction law revised by Nagata et al. (2012, https://doi.org/10.1029/2011JB008818). For a situation in which earthquakes occurred repeatedly, we applied dynamic sinusoidal stress perturbation. The stress perturbation caused an increase in slip velocity after the cessation of perturbation, and the resultant slip weakened the frictional strength. This leads to dynamic earthquake triggering for certain perturbation amplitudes. The following results were obtained. (1) Dynamic perturbations of long durations have high triggering potentials, whereas there is no significant frequency dependence because the potential is mainly determined by the total displacement due to the perturbation. (2) When a static stress jump is applied in addition to a dynamic perturbation, their combined effect on the triggering potential cannot be estimated by simply summing the applied stress amplitudes. A lower bound can be found by summing the logarithms of the velocity changes due to each individual perturbation. In addition, a nonlinear effect is required to explain the simulation results. (3) We evaluate the equivalent static stress jump that results in a triggering potential approximately the same as in the case of dynamic stress perturbation. (4) Even if the static stress change is negative, large dynamic stress perturbations can trigger earthquakes. (5) When stress perturbations are applied to stably sliding patches, dynamic triggering can occur under certain conditions.