Aftershocks Preferentially Occur in Previously Active Areas

Abstract The clearest statistical signal in aftershock locations is that most aftershocks occur close to their mainshocks. More precisely, are triggered at distances following a power-law decay distance (Felzer and Brodsky, 2006). This kernel used epidemic-type sequence (ETAS) modeling typically assumed be isotropic, even though individual sequences show more clustered occurrence. assumption of spatially isotropic triggering kernels can impact the estimation ETAS parameters themselves, such as biasing magnitude-productivity term, alpha, assigning too much weight secondary rather than primary (direct) triggering. Here we southern California, all mainshock–aftershock distances, preferentially areas previous seismicity. For given sequence, scaling between rates seismicity rate approximately linear. However, total number observed for independent background rate. We explain both these observations within framework rate-and-state friction (Dieterich, 1994).