Modeling rupture propagation into creeping faults by thermal pressurisation

Victor Vescu, Oliver Stephenson, & Nadia Lapusta

Submitted September 8, 2024, SCEC Contribution #14006, 2024 SCEC Annual Meeting Poster #157

Different sections of faults, like the San Andreas (SAF), accommodate stress via stick-slip under velocity-weakening friction or through gradual creep in a velocity-strengthening regime. When a rupture reaches a region of slow slip, thermal pressurisation of pore fluids can enable rapid weakening and dynamic failure of the creeping zone (Noda and Lapusta, Nature, 2013). We explore whether a theoretical Mw 7.2 earthquake, which propagates towards the creeping section, could generate enough thermal pressurisation to rupture through the creeping section, building upon recent observations that the creeping section of the SAF may have experienced large seismic slip (Coffey et al., Geology, 2022). At the same time, the 2004 Mw 6 Parkfield earthquake did not significantly propagate into the creeping section. The highly simplified model of the simulated fault consists of locked (VW) and creeping (VS) segments, depth-averaged to consider only variations with its length and embedded within a 2-D linearly elastic isotropic medium. The fault is governed by a logarithmic rate-and-state friction law. The VS section additionally has thermal pressurisation (TP) of pore fluids due to shear heating, with the diffusion of heat and fluids from the fault. We vary three thermal pressurisation parameters (the coupling coefficient between temperature and pore pressure change, hydraulic diffusivity, and half-width of the actively shearing layer) and the effect of the off-fault inelasticity to find the combinations that lead to dynamic rupture through the creeping region when the event size is large enough. Our preliminary results indicate that there are indeed plausible parameter combinations for which Mw 6 events arrest, but Mw 7.2 events dynamically rupture the creeping segment. However, the corresponding models have temperatures exceeding melting values in the VW section where (following previous models) TP is not active. In addition, the average slip rates are too high compared to most observations. Our current work is directed towards exploring models with TP on the entire fault and lower slip rates.

Key Words
Thermal Pressurization, Parkfield, Rate-and-State Friction, Dynamic Weakening

Citation
Vescu, V., Stephenson, O., & Lapusta, N. (2024, 09). Modeling rupture propagation into creeping faults by thermal pressurisation. Poster Presentation at 2024 SCEC Annual Meeting.

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