Slide‐Hold‐Slide Protocols and Frictional Healing in Discrete Element Method (DEM) Simulations of Granular Fault Gouge

Ferdowsi, Behrooz; Rubin, Allan M.

doi:10.1029/2021jb022125

Cited by 3 publications

(2 citation statements)

References 83 publications

(273 reference statements)

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“…Additionally, if asperity creep were responsible for the rapid healing it would be expected that the gouge would also exhibit a linear log‐time compaction relationship during the hold period (Sleep, 2006), which we do not observe in our mechanical data (Figures 5e and 5f); the log‐time compaction relationship in our experiments is particularly non‐linear during the initial stages of the hold period when the rapid healing occurs ( t h < 20 s). This observation potentially supports the suggestion from recent granular fault gouge simulation studies that fault healing can be decoupled from changes in gouge layer thickness due to compaction/dilation (Ferdowsi & Rubin, 2020, 2021). Based on the rationale outlined above we believe that, although asperity creep may be operating during the static hold period, it is unlikely that an increase in the real contact area is the dominant cause of the rapid restrengthening we observe in our high‐velocity SHS experiments.…”

Section: Discussionsupporting

confidence: 87%

Rapid Fault Healing After Seismic Slip

2023

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Faults slip suddenly during earthquakes, accelerating to velocities on the order of a few meters per second. At these seismic slip velocities, a significant reduction in fault strength occurs (Di Toro et al., 2011) as a result of various dynamic weakening mechanisms becoming activated by shear heating and/or grain size reductions (Tullis, 2015). Although our knowledge of dynamic fault weakening processes has increased significantly over the last 25 years since the advent of high-velocity friction experiments (Tsutsumi & Shimamoto, 1997), our understanding of how faults regain their strength after dynamic weakening, once seismic slip has ceased, is more limited. Fault restrengthening is a fundamental process in the earthquake cycle that may control the recurrence time (Vidale et al., 1994), the mode of slip (Shreedharan et al., 2023), the maximum strength that can be attained (Kanamori & Allen, 1986;Scholz et al., 1986), and the nature of radiated energy (McLaskey et al., 2012) in future events.The rate of fault restrengthening can vary with both time and space along a fault during the earthquake cycle (Li et al., 2006;Pei et al., 2019). Restrengthening may occur initially during coseismic slip itself, as sometimes observed during the deceleration phase of high-velocity friction experiments (e.g.,

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Section: Discussionsupporting

confidence: 87%

Rapid Fault Healing After Seismic Slip

2023

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“…These observations may indicate that the interface undergoes structural changes during the rapid stress increase of the reslide, changes that are not captured by any existing state-evolution formulation. Insight into these changes might come from granular flow simulations, which have successfully reproduced several aspects of laboratory rock and gouge friction experiments ( 50 , 53 ), and examination of the time-dependent normal displacement across the sliding surface. Nonetheless, the Slip formulation appears to do a better job of matching the peak friction during the reslides than the Aging formulation, which predicts that

, when plotted versus

), has a slope of b , which is well constrained by our velocity steps.…”

Section: Discussionmentioning

confidence: 99%

The evolution of rock friction is more sensitive to slip than elapsed time, even at near-zero slip rates

Bhattacharya

Rubin

Tullis

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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Nearly all frictional interfaces strengthen as the logarithm of time when sliding at ultra-low speeds. Observations of also logarithmic-in-time growth of interfacial contact area under such conditions have led to constitutive models that assume that this frictional strengthening results from purely time-dependent, and slip-insensitive, contact-area growth. The main laboratory support for such strengthening has traditionally been derived from increases in friction during “load-point hold” experiments, wherein a sliding interface is allowed to gradually self-relax down to subnanometric slip rates. In contrast, following step decreases in the shear loading rate, friction is widely reported to increase over a characteristic slip scale, independent of the magnitude of the slip-rate decrease—a signature of slip-dependent strengthening. To investigate this apparent contradiction, we subjected granite samples to a series of step decreases in shear rate of up to 3.5 orders of magnitude and load-point holds of up to 10,000 s, such that both protocols accessed the phenomenological regime traditionally inferred to demonstrate time-dependent frictional strengthening. When modeling the resultant data, which probe interfacial slip rates ranging from 3 . μ m · s − 1 . to less than 10 − 5 μ m · s − 1 , we found that constitutive models where low slip-rate friction evolution mimics log-time contact-area growth require parameters that differ by orders of magnitude across the different experiments. In contrast, an alternative constitutive model, in which friction evolves only with interfacial slip, fits most of the data well with nearly identical parameters. This leads to the surprising conclusion that frictional strengthening is dominantly slip-dependent, even at subnanometric slip rates.

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