GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 is associated with formation of new weak minerals (clays) and weak water bonds in the slipping zone. Fault healing rate β = Δ μ /log t hold or the change of the static friction coefficient Δ μ with log time, is a significant parameter in the seismic cycle as it controls the ability of the fault wall rocks to store elastic strain energy. We performed slide-hold-slide (holds lasted up to five days) experiments with pressurized water from room ( T = 20°C) to high temperature (e.g., T = 400°C) conditions. At room temperature, β > 0 as in experiments conducted in the past. Instead, when water is at higher temperatures and at the liquid and supercritical states, β switches from positive to negative with increasing hold time. We speculate that the transition, which may result in nature also in the switch from seismic to aseismic fault behavior, could be related to the formation of new mineral assemblages associated with fluid-rock interaction. These new experimental results, obtained under extreme but typical water conditions at earthquake hypocentral depths, challenge our knowledge of rock friction properties based on more conventional experiments and may lead to a novel understanding of the seismic cycle in geothermal systems. *Giulio Di Toro (email: giulio.ditoro@unipd.it ; tel. +39 049 827905 )