Assessing the efficiency of thermal pressurisation using natural pseudotachylyte-bearing rocks

TL;DR

This study evaluates the effectiveness of thermal pressurisation in fault weakening by combining field measurements of fault rocks with numerical simulations, highlighting the critical role of damage-induced property changes during earthquakes.

Contribution

It provides new insights into how damage processes alter fault rock properties, affecting thermal pressurisation efficiency and dynamic weakening during earthquakes.

Findings

Melting occurs only with damaged rock properties.

A tenfold increase in permeability enables melting.

Damage significantly influences fault weakening mechanisms.

Abstract

The efficiency of thermal pressurisation as a dynamic weakening mechanism relies on the thermal and hydraulic properties of the rocks forming the fault core. Here, we assess the effectiveness of thermal pressurisation by comparing predictions of temperature rise to field estimates based on pseudotachylyte-bearing rocks. We measure hydraulic and transport properties of a suite of fault rocks (a healed cataclasite, an unhealed breccia and the intact parent rock) from the pseudotachylyte-bearing Gole Larghe fault in the Adamello batholith (Italy), and use them as inputs in numerical simulations of thermal pressurisation. We find that the melting temperature can be reached only if damaged, unhealed rock properties are used. A tenfold increase in permeability, or a fourfold increase in pore compressibility of the intact rock is required to achieve melting. Our results emphasise the importance of damage processes that strongly modify fault rock properties and dynamic weakening processes during earthquake propagation.