Aftershocks due to property variations in the fault zone: A mechanical model

Abstract

Studies of many large strike-slip earthquakes have shown that the seismicity rate increases in quadrants in which the Coulomb stress is increased by the earthquake rupture. This mechanism explains the concentration of aftershocks near the tips of the fault rupture, but cannot explain the aftershocks on the sides of the rupture zone, where the aftershocks are commonly abundant. We suggest that these aftershocks may be induced by variations of fault-zone properties not included in the previous models. In a finite-element model that treats the rupture plane as a zone with heterogeneous physical properties, as suggested by field observations and laboratory experiments, the Coulomb-stress changes triggered by the mainshock no longer uniformly decrease on the sides of the rupture zone, but show complex patterns of negative and positive changes. These results may explain some of the aftershocks on the sides of the mainshock rupture.