Earthquake Nucleation along Faults with Heterogeneous Weakening Rate

TL;DR

This paper develops an analytical framework combining nucleation theory and physics concepts to understand how heterogeneities in fault weakening rates influence earthquake nucleation, revealing three distinct instability regimes.

Contribution

It introduces a novel analytical model predicting nucleation length variations due to heterogeneities, validated by 2D dynamic simulations, and identifies three instability regimes.

Findings

Three instability regimes identified: local, extremal, and homogenized.

Heterogeneities at scales smaller than nucleation length can be effectively averaged.

Model predictions align with simulation measurements of nucleation lengths.

Abstract

The transition from quasi-static 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 $L_c$ 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.