Where did the time go? The remarkable slip-sensitivity of friction at near-zero slip rates

Pathikrit Bhattacharya, Allan M. Rubin, Terry E. Tullis, N. M. Beeler, & Keishi Okazaki

In Preparation October 17, 2019, SCEC Contribution #9952

The frequently-used constitutive formulations of rate- and-state dependent friction offer two end-member views on whether friction evolves only with slip (Slip state evolution) or with time even without slip (Aging state evolution). While traditional velocity stepping experiments show support for the Slip equation, frictional interfaces have traditionally been interpreted as undergoing purely time-dependent increases in frictional strength at the extremely low slip rates accessed during slide-hold-slide experiments. Given that large velocity step decreases and slide-hold-slide experiments both probe frictional strengthening in response to rapid and large decreases in slip rate, this seems paradoxical. In this study, we investigate this apparent paradox by performing a series of extreme velocity step decreases (up to 3.5 orders of magnitude) and holds up to 10000 s during the same experimental run. We find that the Aging equation consistently fails to fit these data and requires parameters which differ by orders of magnitude between the different sliding conditions. In contrast, the Slip equation fits the entire dataset equally well with nearly identical parameters throughout, even when the slip rates are estimated to be smaller than 10−5μms−1. We also demonstrate that the Aging equation’s failure to explain these data arises from its prediction of purely time-dependent strengthening under such rapid and large reductions in slip rate, which is precisely the portion of parameter space where Aging equation style time-dependent strengthening had traditionally been considered most appropriate.

Citation
Bhattacharya, P., Rubin, A. M., Tullis, T. E., Beeler, N. M., & Okazaki, K. (2019). Where did the time go? The remarkable slip-sensitivity of friction at near-zero slip rates. Proceedings of the National Academy of Sciences, (in preparation).

Related Projects & Working Groups
Fault and Rupture Mechanics