Effect of Fluids on Friction Properties and Stability of Rock Gouge

Taeho Kim, Nadia Lapusta, Daniel Faulkner, & John Bedford

Published September 11, 2022, SCEC Contribution #12598, 2022 SCEC Annual Meeting Poster #182

Earthquake ruptures on pre-existing natural faults occur as shear deformation – or slip - in layers of fault gouge. The shear resistance of fault gouge to slip is a key ingredient in how the earthquake ruptures nucleate, propagate, and arrest. We seek to better understand the shear resistance of fault gouge by modeling laboratory experiments on its frictional response to steps in slip velocity under compression and pore fluid pressure (Bedford et al., Nature Comm., 2022). In particular, the velocity-step experiments on quartz gouge between 0.3 and 3 microns/s reveal evolving rate-and-state properties with slip, with initially velocity-strengthening friction evolving to velocity-weakening friction that results in stick-slip for the faster slip velocity. The slip events are different for the quartz gouge under pore fluid pressure and room-dry, despite the same value of the effective normal stress in the two cases. The slip events with the pressurized pore fluids have similar stress drop but larger recurrence times, indicating the presence of significant aseismic slip compared to the dry case and hence more stable behavior. These result point to significant fluid effects on frictional sliding beyond the classical formulation of rate-and-state friction with effective normal stress. We examine possible mechanisms for such behavior through numerical simulations of the experiments using both single-degree-of-freedom spring-slider approximations and finite-fault models. Two possibilities are the stabilizing effect of inelastic shear-induced dilatancy through pore pressure transients and different rate-and-state properties in the presence of fluids. We find that slip stabilization through pore-pressure transients due to dilatancy is unlikely to be the source of the larger amount of creep in pressurized experiments, since all our simulations with dilatancy-induced pore pressure variations result in reduction of both stress drop and recurrence time of the stick-slip events compared to cases with no pore fluid pressure and the same rate-and-state properties, unlike the experimental observations. Hence matching the experimental results likely requires different rate-and-state properties of gouge in the presence of fluids, in contrast to typical fault modeling assumptions. We will report on our current work on modeling the experimental results with different state evolution laws and examining the potential role of compaction.

Key Words
Stability of Gouge Layers, Frictional Sliding under Presence of Fluids

Citation
Kim, T., Lapusta, N., Faulkner, D., & Bedford, J. (2022, 09). Effect of Fluids on Friction Properties and Stability of Rock Gouge. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)