Dynamic weakening during earthquakes controlled by fluid thermodynamics

M Acosta,A Schubnel,F X Passelègue,M Violay

doi:10.1038/s41467-018-05603-9

Abstract

Earthquakes result from weakening of faults (transient decrease in friction) during co-seismic slip. Dry faults weaken due to degradation of fault asperities by frictional heating (e.g. flash heating). In the presence of fluids, theoretical models predict faults to weaken by thermal pressurization of fault fluid. However, experimental evidence of rock/fluid interactions during dynamic rupture under realistic stress conditions remains poorly documented. Here we demonstrate that the relative contribution of thermal pressurization and flash heating to fault weakening depends on fluid thermodynamic properties. Our dynamic records of laboratory earthquakes demonstrate that flash heating drives strength loss under dry and low (1 MPa) fluid pressure conditions. Conversely, flash heating is inhibited at high fluid pressure (25 MPa) because water’s liquid–supercritical phase transition buffers frictional heat. Our results are supported by flash-heating theory modified for pressurized fluids and by numerical modelling of thermal pressurization. The heat buffer effect has maximum efficiency at mid-crustal depths (~2–5 km), where many anthropogenic earthquakes nucleate.

Highlights

Earthquakes result from weakening of faults during co-seismic slip
Highfrequency records[9,10] (Fig. 1b–d) showed that τ first increased from τ0 up to a peak dynamic value τp and abruptly dropped to a minimum dynamic value τmin before recovering to τf, thereby defining a dynamic stress drop (Δτb = τp − τmin)
The dynamic rise of τ up to τp resulted from stress amplification at the rupture tip[20]

Summary

Introduction

Earthquakes result from weakening of faults (transient decrease in friction) during co-seismic slip. Our experimental conditions, we considered water cooling of asperities as a purely diffusive mechanism (no advection) for fault permeabilities

Results

Conclusion