Stability of Rock Gouge in the Presence of Fluids

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

Published September 10, 2023, SCEC Contribution #13167, 2023 SCEC Annual Meeting Poster #066

Earthquake ruptures on pre-existing natural faults occur as shear deformation – or slip - in layers of fault gouge composed of grains with the characteristic length of microns. The shear resistance of fault gouge to slip and how it evolves with the complex deformation stages of granular materials is a key ingredient in how the earthquake ruptures nucleate, propagate, and arrest. Despite its ubiquity in fault systems, gouge with small grain sizes is often avoided in laboratory experiments due to its inherent instability and the lack of existing methods to infer quantitative information from stick-slip signals. Here, we model laboratory experiments of unstable gouge and its frictional response to steps in slip velocity under compression and pore fluid pressure using single-degree-of-freedom spring slider representations. The experiments demonstrate both gradual development of instability with slip and abrupt transitions in response to velocity steps. We couple the forward model to a combination of Bayesian inference and objective minimization methods to infer physical properties of the gouge with uncertainty quantification at various stages of deformation. We find that the combination of rate-and-state frictional parameters b-a and DRS can be constrained relatively well by conventional recordings of stick-slip signals while a and b are difficult to narrow down individually due to the high non-linearity and non-uniqueness of system. We also infer that the development of instability is accompanied by a decrease in the characteristic slip distance, DRS, which is further associated with significant reduction of the grain size at the localized shear layer as evidenced by SEM images of the microstructure. The methods allow, for the first time, inference of rate-and-state frictional parameters from stick-slip data, and the possibility of tracking the evolution of frictional parameters with slip in a single experiment.

Key Words
Frictional Stability, Granunlar Gouge

Citation
Kim, T., Lapusta, N., Faulkner, D., & Bedford, J. (2023, 09). Stability of Rock Gouge in the Presence of Fluids. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology