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Modeling Intermittent Rupture in Fault Gouge Using Velocity-Strengthening Rate-and-State Friction with Flash Heating

Description: 

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 rock 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 find that such a simulated gouge region with initially rate-strengthening friction is indeed able to first arrest the dynamic slip upon its arrival, and to subsequently re-nucleate another slip event within this region due to flash-heating-like dynamic weakening, although at a different location. The simulation results indicate that whether the dynamic weakening in gouge can occur within the observing window strongly depends on the initial value of state variable. 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 findings support the developing concept that co-seismic weakening may enable earthquake rupture to break through initially stable fault regions, with significant implications for seismic hazard.

Session: Numerical Modeling in Seismology: Developments and Applications

Type: Oral

Date: 4/20/2023

Presentation Time: 02:00 PM (local time)

Presenting Author: Nadia Lapusta

Student Presenter: No

Invited Presentation: 

Authors