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 (SH) protocols. A few slide-hold-slide (SHS) 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 Discrete Element Method (DEM) model in SH and SHS 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 SH 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 to 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.

中文翻译：

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颗粒断层泥离散元法 (DEM) 模拟中的滑动-保持-滑动协议和摩擦愈合

速率和状态相关摩擦 (RSF) 的经验本构建模框架通常用于描述断层泥对稳定滑动扰动的时间相关摩擦响应。在之前的一项研究 (Ferdowsi & Rubin, 2020) 中，我们发现断层剪切带的基于颗粒物理的模型在接触尺度上具有与时间无关的特性，再现了实验室岩石和凿岩摩擦实验的速度现象学步和滑动保持 (SH) 协议。一些幻灯片保持幻灯片 (SHS) 模拟进一步表明，粒度模型在描述实验室数据方面可能优于当前的经验 RSF 定律。在这里，我们探索了 SH 和 SHS 协议中相同离散元方法 (DEM) 模型在各种滑动速度、保持持续时间和系统刚度下的行为，并为这一观点提供额外的支持。我们发现，与实验室数据类似，SH 模拟过程中的应力衰减率与 RSF 方程的“滑移定律”版本大体一致，使用独立于速度阶跃测试确定的参数值。在长时间保持后的重新滑动期间，该模型与实验室数据类似，在对数保持时间产生几乎恒定的摩擦愈合速率，该速率在 RSF“状态演化”参数的 0.5 到 1 倍范围内乙。我们还发现，在实验室实验中，颗粒层在保持期间经历对数时间压实。这与老化定律下状态演化的传统理解是一致的，即使相关的应力衰减与滑移而不是老化定律预测的相似。