Modeling intermittent laboratory earthquakes in fault gouge using rate-and-state friction with flash heating

Shengduo Liu, Nadia Lapusta, Vito Rubino, & Ares J. Rosakis

Published September 11, 2022, SCEC Contribution #12226, 2022 SCEC Annual Meeting Poster #140

Destructive earthquake ruptures on natural faults occur as dynamic slip in layers of a fine granular material known as the fault gouge. An experimental study of earthquake ruptures within a Homalite-100 interface with fault gouge material has revealed the occurrence of complicated slip events, during which the dynamic slip initially arrests when it enters the fault gouge, then spontaneously and repeatedly re-nucleates and arrests within the gouge region (Rubino et al., Nature, 2022). The repeated strengthening and dramatic weakening of the fault gouge inferred by these experiments suggests that this behavior is due to velocity-strengthening properties at lower slip rates and dynamic weakening, reminiscent of flash heating, at higher slip rates.

To verify the conjectures based on the experiments and to better understand the friction behavior within the fault gouge, we conduct 3-D finite-element simulations motivated by the lab experiments. In the experimental setup, dynamic ruptures are nucleated within the Homalite-100 interface and propagate there for a while before entering the fault gouge region. We assign velocity-weakening and velocity-strengthening rate-and-state properties to the Homalite-100 and gouge interface at low slip rates, respectively, coupled with strong dynamic-weakening effect at high slip rates. We find that the velocity-strengthening rate-and-state friction coupled with strong flash-heating dynamic-weakening effect in the gouge region, is indeed able to first arrest the dynamic slip upon its arrival, and to subsequently re-nucleate another slip event within this region. The flash-heating-like dynamic weakening is crucial for the re-nucleation of slip events. The simulation results indicate that whether the dynamic weakening can occur within the observing window strongly depends on the initial value of state variable within the gouge region. The simulations also reveal complex interactions between rupture on the Homalite-100 interface and the initially barrier-like gouge region, with the slip arrest in the gouge region propagating backward into the Homalite-100 interface, before the rupture elsewhere overtakes the rupture arrest and propagates forward into the gouge region again. Our current work focuses on understanding whether the full set of experimental observations can be reproduced with homogeneous conditions within the gouge region, or whether some heterogeneity is required to reproduce the observed behavior.

Key Words
Friction, dynamic weakening, dynamic rupture simulations, rupture arrest, earthquake nucleation

Citation
Liu, S., Lapusta, N., Rubino, V., & Rosakis, A. J. (2022, 09). Modeling intermittent laboratory earthquakes in fault gouge using rate-and-state friction with flash heating. Poster Presentation at 2022 SCEC Annual Meeting.

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