Exploring models of foreshock sources using rate-and-state friction

Abstract eng:
Many large earthquakes are preceded by foreshocks, which are understood to occur within the nucleating region of the mainshock. How are these precursory events able to occur without immediately triggering the larger event? In this study, earthquake nucleation is investigated numerically via simulations of earthquake cycles with foreshocks occurring on a rate-and-state fault. Inspired by the asperity interpretation of foreshock sources from laboratory observations, the models presented here have heterogeneous fault properties with patches that are under higher compression and/or smoother. In this unique model, mainshocks occur in the larger-scale velocity-weakening region and foreshocks can occur on the embedded patches. The results show that the rate-and-state models of foreshock sources are suitable for producing isolated foreshocks under the right conditions of scale separation. In addition, despite the wide variation in patch parameters implemented, remarkably, stress drops of the foreshocks are consistent with laboratory and field observations and are approximately constant.

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