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

Abstract

AbstractWe perform physics‐based simulations of earthquake rupture propagation on geometrically complex strike‐slip faults to examine the off‐fault stress changes resulting from dynamic fault slip. We consider many different realizations of the fault profile and use the output of our simulations to calculate the Coulomb failure function (CFF) for each realization. We analyze the effects of fault maturity as well as the self‐affine character of the fault surface on the stress field. To quantify our results, we calculate the probability density function for the CFF as a function of distance and observe that the CFF values show a greater variability in the near‐fault region (distance <3 km away from fault), and this spread squeezes into a narrow negative range in the far‐field region. In the near‐fault region, we see many zones of positive CFF change, which are not observed in the far‐fault region. We consider these zones of CFF increase as locations of potential aftershocks and compare their size with rupture areas of aftershocks from relocated earthquake catalogs of Northern and Southern California. Our model results and observational data show a relatively high probability of occurrence of smaller potential aftershock areas compared to larger ones in the near‐fault region. Additionally, based on our comparison with aftershock and preshock data, we conclude that the stresses in the near‐fault region are dominated by fault roughness effects. Our results suggest that tectonic stresses are highly spatially heterogeneous, and this complexity persists throughout seismic cycle.