Unstable slip pulses and earthquake nucleation as a non-equilibrium first-order phase transition

TL;DR

This paper models earthquake nucleation as a non-equilibrium first-order phase transition, identifying unstable slip pulses as critical nuclei that trigger rapid slip, supported by analytical and numerical evidence.

Contribution

It introduces a novel analogy between earthquake nucleation and phase transitions, highlighting unstable slip pulses as critical nuclei in a non-equilibrium framework.

Findings

Unstable slip pulses act as critical nuclei for rapid slip.

Existence of a nucleation length $L^*$ in 2D systems.

A Griffith-like length $L_G$ influences slip pulse dynamics.

Abstract

The onset of rapid slip along initially quiescent frictional interfaces, the process of `earthquake nucleation', and dissipative spatiotemporal slippage dynamics play important roles in a broad range of physical systems. Here we first show that interfaces described by generic friction laws feature stress-dependent steady-state slip pulse solutions, which are unstable in the quasi-1D approximation of thin elastic bodies. We propose that such unstable slip pulses of linear size $L^*$ and characteristic amplitude are `critical nuclei' for rapid slip in a non-equilibrium analogy to equilibrium first-order phase transitions, and quantitatively support this idea by dynamical calculations. We then perform 2D numerical calculations that indicate that the nucleation length $L^*$ exists also in 2D, and that the existence of a fracture mechanics Griffith-like length $L_G\!<\!L^*$ gives rise to a richer phase-diagram that features also sustained slip pulses.