Frictional heating processes and energy budget during laboratory earthquakes

TL;DR

This study investigates the energy budget of laboratory earthquakes, focusing on frictional heating and its relation to seismic radiation efficiency, revealing how fault strength and asperities influence energy dissipation and wave radiation.

Contribution

It provides the first full energy budget analysis of laboratory earthquakes, linking frictional heating, fault strength, and seismic radiation efficiency.

Findings

Frictional heating can be mapped using in-situ carbon thermometry.

Increasing radiation efficiency correlates with thermal weakening of faults.

Fault strength transition affects asperity behavior and energy radiation.

Abstract

During an earthquake, part of the released elastic strain energy is dissipated within the slip zone by frictional and fracturing processes, the rest being radiated away via elastic waves. Frictional heating thus plays a crucial role in the energy budget of earthquakes, but, to date, it cannot be resolved by seismological data. Here we investigate the dynamics of laboratory earthquakes by measuring frictional heat dissipated during the propagation of shear instabilities at typical seismogenic depth stress conditions. We perform, for the first time, the full energy budget of earthquake rupture and demonstrate that increasing the radiation efficiency, i.e. the ratio of energy radiated away via elastic waves compared to that dissipated locally, increases with increasing thermal - frictional - weakening. Using an in-situ carbon thermometer, we map frictional heating temperature heterogeneities - 'heat' asperities - on the fault surface. Combining our microstructural, temperature and mechanical observations, we show that an increase in fault strength corresponds to a transition from a weak fault with multiple strong asperities, but little overall radiation, to a highly radiative fault, which behaves as a single strong asperity.