Sequences of seismic and aseismic slip on bimaterial faults show dominant rupture asymmetry and potential for elevated seismic hazard

We perform numerical simulations of sequences of earthquake and aseismic slip on planar rate and state faults separating dissimilar material within the 2-D plane strain approximation. We resolve all stages of the earthquake cycle from aseismic slip to fast ruptures while incorporating full inertia effects during seismic event propagation. We show that bimaterial coupling results in favorable nucleation site and subsequent asymmetric rupture propagation. We demonstrate that increasing the material contrast enhances this asymmetry leading to higher slip rates and normal stress drops in the preferred rupture propagation direction. The normal stress drop, induced by the bimaterial effect, leads to strong dynamic weakening of the fault and may destabilize the creeping region on a heterogeneous rate and state fault, resulting in extended rupture propagation. Such rupture penetration into creeping patches may lead to more frequent opening of earthquake gates, causing increased seismic hazard. Furthermore, bimaterial coupling may lead to irregular seismicity pattern in terms of event length, peak slip rates, and hypocenter location, depending on the properties of the creeping patches bordering the seismogenically active part of the fault. Our results highlight robust characteristics of bimaterial interfaces that persist over long sequence of events and suggest the need for further exploration of the role of material contrast in earthquake physics and models of seismic hazard.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study conducts numerical simulations of earthquake and aseismic slip on fault interfaces with dissimilar materials. The results demonstrate that the bimaterial coupling leads to favorable nucleation site and asymmetric rupture propagation. Increasing material contrast enhances this asymmetry, resulting in higher slip rates and normal stress drops. The normal stress drop induced by bimaterial effect can weaken the fault and extend the rupture propagation, leading to increased seismic hazard. These findings underscore the robust characteristics of bimaterial interfaces and suggest further exploration of the role of material contrast in earthquake physics and models of seismic hazard.