Numerical Modeling of a Fluid-Induced Aseismic-Seismic Slip Sequence on a Rate-and-State Fault

Stacy Larochelle, Nadia Lapusta, Jean-Paul Ampuero, & Frederic Cappa

Published August 7, 2018, SCEC Contribution #8311, 2018 SCEC Annual Meeting Poster #186

Numerous activities in the geo-energy industry (e.g., hydraulic fracking, wastewater disposal, CO2 sequestration and enhanced geothermal systems) involve fluid injections into the shallow crust (~1 to 5 km depth). That these fluid injections can induce fault slip (either seismic or aseismic) is now well recognized from surface and borehole observations. When injected directly into a fault system, fluids decrease fault strength by increasing pore pressure. This strength drop may in turn result in seismic or aseismic slip. However, what conditions promote stable versus unstable failure, and the exact physical mechanisms at play are still poorly understood. For example, the fluid-injection field experiment described by Guglielmi et al. (Science, 2015) resulted in aseismic slip first, followed by a sequence of 80 seismic events (i.e. microearthquakes), with the initial aseismic slip attributed to velocity-strengthening rate-and-state properties based on a spring-slider model. In this study, we seek to determine the range of frictional regimes consistent with the experimental observations through numerical simulations of slip on a fault in a continuum medium. Specifically, we simulate slip on a rate-and-state fault embedded in a homogeneous elastic medium and subjected to increasing pore pressure at the injection site, with the fault and pore pressure parameters informed by the Guglielmi et al.’s study. We use an elastodynamic boundary-integral code supplemented with fluid pressure diffusion along the fault. We find that fault models with velocity-weakening friction can explain the initial aseismic slip as well as the velocity-strengthening ones. Constraining the frictional parameters further would require more experimental studies with simultaneous measurements of fluid pressure, fault-normal and fault-parallel displacements, and seismicity, both at the injection site and in its surroundings.

Citation
Larochelle, S., Lapusta, N., Ampuero, J., & Cappa, F. (2018, 08). Numerical Modeling of a Fluid-Induced Aseismic-Seismic Slip Sequence on a Rate-and-State Fault. Poster Presentation at 2018 SCEC Annual Meeting.

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