Dynamic weakening by acoustic fluidization during stick-slip motion

TL;DR

This study validates acoustic fluidization as a mechanism for fault weakening during earthquakes, showing that acoustic waves at specific frequencies can induce failure and are spontaneously generated at slip initiation.

Contribution

The paper provides numerical evidence supporting acoustic fluidization as a key process in fault weakening and earthquake triggering, highlighting the role of characteristic frequency oscillations.

Findings

Perturbations at a specific frequency influence slip dynamics.

Spontaneous acoustic waves emerge at failure onset.

Weakening correlates with acoustic wave activity.

Abstract

The unexpected weakness of some faults has been attributed to the emergence of acoustic waves that promote failure by reducing the confining pressure through a mechanism known as acoustic fluidization, also proposed to explain earthquake remote triggering. Here we validate this mechanism via the numerical investigation of a granular fault model system. We find that the stick-slip dynamics is affected only by perturbations applied at a characteristic frequency corresponding to oscillations normal to the fault, leading to gradual dynamical weakening as failure is approaching. Acoustic waves at the same frequency spontaneously emerge at the onset of failure in absence of perturbations, supporting the relevance of acoustic fluidization in earthquake triggering.