Shear localisation controls the dynamics of earthquakes

TL;DR

This paper demonstrates through numerical simulations that shear localisation significantly influences earthquake rupture dynamics, revealing a scaling law between localisation width and rupture speed, and suggesting earthquakes are linked to extreme strain localisation.

Contribution

It introduces a dual-scale simulation approach coupling fault microphysics with elastodynamics, showing shear localisation's critical role in earthquake propagation and energy dissipation.

Findings

Shear localisation leads to classical crack-like ruptures.

Fracture energy is lower with shear localisation than uniform shearing.

A unique scaling law relates localisation width to rupture speed.

Abstract

Earthquakes are produced by the propagation of rapid slip along tectonic faults. The propagation dynamics is governed by a balance between elastic stored energy in the surrounding rock, and dissipated energy at the propagating tip of the slipping patch. Energy dissipation is dictated by the mechanical behaviour of the fault, which is itself the result of feedbacks between thermo-hydro-mechanical processes acting at the mm to sub-mm scale. Here, we numerically simulate shear ruptures using a dual scale approach, allowing us to couple a sub-mm description of inner fault processes and km-scale elastodynamics, and show that the sudden localisation of shear strain within a shear zone leads to the emergence of classical cracks driven by a constant fracture energy. The fracture energy associated to strain localisation is substantially smaller than that predicted assuming uniform shearing. We show the existence of a unique scaling law between the localised shearing width and the rupture speed. Our results indicate that earthquakes are likely to be systematically associated to extreme strain localisation.