Thermal weakening friction during seismic slip: experiments and models with heat sources and sinks

Abstract

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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).…”

Earthquake dynamics constrained from laboratory experiments: new insights from granular materials

“…The considered models are quite representative of two rather different classes of constitutive laws, the slipdependent and the rate and state friction. Of course, in the literature different models have been proposed, but since the observed stress reduction on our granular experiments is not dramatic, we do not consider other governing equations proposed in the recent literature, which account for large friction reduction at high speed [see for instanceNielsen et al, 2021]. It is important to mention that in a separate paper we will try to construct a mathematical model able to describe the data arising from experiments on granular materials, possibly resorting to microphysical models [Van der Ende et al, 2018].We want to emphasize that the fitting procedure presented here (see section 3) is totally novel and it represents the first attempt to fit the friction value of a rate and state function to spontaneous slip; the only other attempt presented in literature, to our knowledge, is the work byBirthe [2015], based on a solid-on-solid experiment, where the parameters are estimated by fitting the velocity, and the 22 % of the considered data could not be fitted satisfyingly with the Dieterich-Ruina model.…”