Slide-hold-slide protocols and frictional healing in a simulated
granular fault gouge
Abstract
The empirical constitutive modeling framework of Rate- and
State-dependent Friction (RSF) is commonly used to describe the
time-dependent frictional response of fault gouge to perturbations from
steady sliding. In a previous study (Ferdowsi & Rubin, 2020), we found
that a granular-physics-based model of a fault shear zone, with
time-independent properties at the contact scale, reproduces the
phenomenology of laboratory rock and gouge friction experiments in
velocity-step and slide-hold protocols. A few slide-hold-slide
simulations further suggested that the granular model might outperform
current empirical RSF laws in describing laboratory data. Here, we
explore the behavior of the same model in slide-hold and
slide-hold-slide protocols over a wide range of sliding velocities, hold
durations, and system stiffnesses, and provide additional support for
this view. We find that, similar to laboratory data, the rate of stress
decay during slide-hold simulations is in general agreement with the
“Slip law” version of the RSF equations, using parameter values
determined independently from velocity step tests. During reslides
following long hold times, the model, similar to lab data, produces a
nearly constant rate of frictional healing with log hold time, with that
rate being in the range of ~0.5 - 1 times the RSF
“state evolution” parameter b. We also find that, as in laboratory
experiments, the granular layer undergoes log-time compaction during
holds. This is consistent with the traditional understanding of state
evolution under the Aging law, even though the associated stress decay
is similar to that predicted by the Slip and not the Aging law.