Effect of Fault Roughness on Aftershock Distribution: Plastic Off‐Fault Material Properties

Abstract

AbstractWe perform spontaneous earthquake rupture simulations on rough strike‐slip faults with off‐fault plastic material properties. We examine the off‐fault stress change and coseismic damage pattern resulting from dynamic fault slip. We use the stress output from each simulation to calculate the Coulomb failure function (CFF). We calculate the CFF values on the extensional and compressional side of the fault using parallel receiver fault orientations. We also calculate the CFF values on the extensional side of the fault using variable receiver fault orientations determined using the angle at which plastic shear strain is maximum. We calculate the probability density function for the CFF values across the fault as a function of distance. We observe a similar overall trend of the CFF values with distance for the extensional and compressional sides—our simulations show a broad range of values in the near‐fault region, while a narrow range of values occurs further from the fault. In the near‐fault region, we observe many more positive CFF change zones using variable receiver fault orientations than using parallel orientations. We calculate the areas and amplitudes of these positive CFF zones as a function of distance away from the fault. Our comparison of CFF amplitudes as a function of rupture area suggests that the spatial aftershock distribution surrounding a fault is controlled by both stress heterogeneity and the coseismic damage zone complexity. The calculations of rupture areas using our model are consistent with ruptured areas of observed aftershocks in California.