Models of fluid-driven seismic swarms with permeability enhancement and rate-and-state friction

Natalia Berrios-Rivera, So Ozawa, & Eric M. Dunham

Published September 8, 2024, SCEC Contribution #13693, 2024 SCEC Annual Meeting Poster #124

Anthropogenic fluid injections and natural fluid flow in Earth’s crust lead to an increase in pore pressure, which can trigger earthquake swarms characterized by a migrating seismicity front. Observations of seismicity expanding with the same diffusive space-time behavior as analytical solutions for aseismic slip have been interpreted as evidence for seismic slip triggered by stress changes from aseismic slip. In some cases, aseismic slip is confirmed from crustal deformation measurements and sheared wellbore casing. Our work offers another interpretation of migrating seismicity that may be relevant when there is no independent evidence for aseismic slip. We show that pressure diffusion and elastic stress transfer can independently drive the diffusive expansion of seismicity fronts, and that analytical solutions for aseismic slip can explain this seismicity pattern, even when all slip is seismic. Here we present a 2D earthquake sequence model that simulates constant-pressure injection into the end of a velocity-weakening rate-and-state fault, permeability enhancement with slip, and fluid transport. Our simulations produce microseismicity concentrated along the slip front and large events that usually rupture back to the injector. While the overall aseismic slip potency is much smaller than the seismic potency, aseismic slip at the leading edge of the slip front appears to be important to increase permeability, allowing fluid influx and pressurization that weakens the fault and prepares it for seismic slip. Although we find that simulations for understressed faults have some distributed seismicity behind the slip edge, most events are concentrated at the slip front, likely due to the planar fault geometry and the uniform friction and stress distributions. Additional simulations with a nonplanar fault introduce heterogeneity in the fault normal stress, resulting in a broader distribution of event sizes, events that rupture both toward and away from the injector, more distributed seismicity behind the leading slip edge, and swarm-like clusters of microseismicity. Even with this complexity, the nonplanar fault sequences produce a diffusively expanding slip front (with fluctuations about this diffusive expansion correlated to the local fault geometry) and mostly seismic slip. Our results suggest that aseismic slip solutions can be used to quantitatively interpret the space-time behavior of migrating swarms, even in cases with negligible aseismic slip.

Citation
Berrios-Rivera, N., Ozawa, S., & Dunham, E. M. (2024, 09). Models of fluid-driven seismic swarms with permeability enhancement and rate-and-state friction. Poster Presentation at 2024 SCEC Annual Meeting.

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