Effect of fault roughness on aftershock distribution: Plastic off-fault material properties

Khurram Aslam

In Preparation January 15, 2018, SCEC Contribution #8988

We perform spontaneous earthquake rupture simulations on rough strike-slip faults with off-fault plastic material properties. The rough faults have a self-similar fractal profile with RMS height of 0.01. We examine the off-fault stress change and damage pattern resulting from dynamic fault slip in the near-fault region. We use the stress output from each simulation to calculate the Coulomb failure function (CFF). We calculate the CFF values at the extensional side of the fault using parallel receiver fault orientations as well as using variable receiver fault orientations determined using the angle at which plastic shear strain is maximum. We calculate and examine the probability density function (PDF) for the CFF values across the fault as a function of distance. We observe that the overall trend of the CFF values with distance remains similar for the extensional and compressional sides – the PDF of CFF shows a broad range of values in the near-fault region and this spread collapses into a narrow range away from the near-fault region, similar to the distribution found for elastic o_-fault properties. In the near-fault region, we observe many positive CFF change zones that are potential locations of aftershocks and we calculate their areas and amplitude as a function of distance away from fault. Our comparison of CFF amplitudes as a function of rupture areas suggests that the spatial aftershock distribution surrounding a fault is controlled by both stress heterogeneity as well as the damage zone complexity. The calculations of rupture areas using our model are consistent with ruptured areas of observed aftershocks in California.

Citation
Aslam, K. (2018). Effect of fault roughness on aftershock distribution: Plastic off-fault material properties. Journal of Geophysical Research, (in preparation).

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)