Thermal Weakening Friction During Seismic Slip: Experiments and Models With Heat Sources and Sinks

Abstract

We test temperature-based models of shear stress against high-velocity friction experiments. 10• Heat sources (friction), sinks (decomposition reactions), and temperature dependence 11 of thermal parameters are included.

Determination of Parameters Characteristic of Dynamic Weakening Mechanisms During Seismic Faulting in Cohesive Rocks

“…It is well known that temperature has a pivotal role in controlling the coseismic shear stress by activating dynamic weakening processes as pointed out in the literature (Di Toro et al., 2011; Nielsen et al., 2021) and further corroborated by our results. However, most of the studies use numerically computed values of expected temperature of the slip zone (see Methods).…”

“…Moreover, our modeling results show that flash heating alone does not explain the subsequent weakening to the dynamic friction level, yielding higher predicted values of dynamic friction for all lithologies. This observation supports the hypothesis that other dynamic weakening mechanisms are necessary to reproduce the inferred stress evolution at the dynamic friction level for experiments performed at these high sliding velocities (Nielsen et al, 2021). Depending on the lithology, melting for silicate-built rocks and diffusion creep for calcitic marble seem to be the most efficient mechanisms, among those here investigated, to explain the measured values of dynamic friction.…”

“…Following Nielsen et al. (2021), the rock thermal diffusivity ( α th ) and thermal conductivity $$\left(\kappa =\frac{{\alpha }_{th}}{\,\rho {C}_{p}}\right)$$ were considered temperature dependent, and the thermal dependence measured experimentally (Hartlieb et al., 2016; Merriman et al., 2018; Miao et al., 2014) was reproduced by adjusting the parameters of an empirical fit function: $$$\kappa ={c}_{c1}\,\mathrm{exp}\left(\frac{T}{{c}_{c2}}\right)+{c}_{c3}$$$ $$${\alpha }_{th}={c}_{a1}\,\mathrm{exp}\left(\frac{T}{{c}_{a2}}\right)+{c}_{a3}$$$ …”

“…However, though it is recognized that dynamic fault weakening is due to both thermally and mechanically activated processes (flash heating, bulk melting, thermal pressurization, viscous flow, etc.) the efficiency of any of these weakening mechanisms is debated and it might be assumed that mechanisms occurring at different temporal and spatial scales control different stages of the weakening phase (Nielsen et al., 2021).…”

Rheology and breakdown energy of a shear zone undergoing flash heating in earthquake-like discrete element models

“…The conceptual micromechanical model for frictional weakening by flash heating supposes that the shear surface consists of a large set of microscopic rock-on-rock asperity contacts subjected to very high stresses (e.g. Rice 2006;Aharonov & Scholz 2018;Nielsen et al 2021). The frictional strength at asperity contacts is defined by the ratio between shear strength and normal stress and varies between 0.6 and 0.8 at low slip rates and temperatures, following Byerlee's friction law.…”