Earthquake Nucleation Along Faults With Heterogeneous Weakening Rate

Abstract

The transition from quasistatic slip growth to dynamic rupture propagation constitutes one possible scenario to describe earthquake nucleation. If this transition is rather well understood for homogeneous faults, how the friction properties of multiscale asperities may influence the overall stability of seismogenic faults remains largely unclear. Combining classical nucleation theory and concepts borrowed from condensed matter physics, we propose a comprehensive analytical framework that predicts the influence of heterogeneities of weakening rate on the nucleation length $L_{\mathrm{c}}$ for linearly slip‐dependent friction laws. Model predictions are compared to nucleation lengths measured from 2D dynamic simulations of earthquake nucleation along heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three instability regimes (local, extremal, and homogenized), each related to different nucleation scenarios, and that the influence of heterogeneities at a scale far lower than the nucleation length can be averaged.

Key Points

• The nucleation length of heterogeneous faults with multiscale asperities of weakening rate can be predicted for slip‐dependent friction

• Our theory accounts for the transition in fault stability regimes from the traditional "weakest defect" theory to a homogenized behavior

• Only asperities larger than the nucleation length participate in the fault stability, while the influence of small asperities is averaged