Elastic stress transfer from seismic slip and fluid pressure diffusion as primary mechanisms controlling slip front expansion in fluid-driven swarm seismicity

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

Submitted September 7, 2025, SCEC Contribution #14652, 2025 SCEC Annual Meeting Poster #TBD

Observations of fluid-driven swarm seismicity expanding with the same diffusive space-time behavior as analytical solutions for aseismic slip have been interpreted as evidence that stress changes from aseismic slip trigger seismic slip. In some cases, aseismic slip is confirmed from crustal deformation measurements or 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 present 2D earthquake sequence models of constant-pressure fluid injection into a velocity-weakening rate-and-state fault, permeability enhancement with slip, and fluid transport. We also derive an analytical solution for a unilateral fluid-driven aseismic shear crack with constant friction and permeability enhancement with slip, a model for pressure diffusion into a fault that extends in one direction from a pressurized layer. This geometry is relevant for some swarms in California, such as the 2016-2019 Cahuilla swarm. The majority of slip is seismic in our simulations, demonstrating that aseismic slip is not the dominant mechanism driving seismicity. Instead, the seismic sequences are driven primarily by fluid pressure diffusion and elastic stress transfer from seismic slip, and these mechanisms act in conjunction with the pre-injection stress state of the fault and injection parameters to modulate the diffusive expansion of the slip front. The seismicity front and total slip distribution in our simulations evolve similarly to analytical solutions for fluid-driven aseismic shear cracks, regardless of whether slip is seismic or aseismic, suggesting that aseismic slip solutions can be used to quantitatively interpret the space-time behavior and slip evolution of migrating swarms. These findings can be applied to swarm seismicity datasets to constrain relative amounts of seismic and aseismic slip if independent model parameter constraints are available, and can be leveraged to develop an efficient inversion framework to estimate parameters such as fault zone permeability and initial stress.
Our findings challenge current ideas about the importance of aseismic slip in fluid-driven swarms. While we focus on diffusively expanding slip fronts in 2D, 3D models with diffusively or non-diffusively expanding slip fronts may also be driven by similar mechanisms. We are currently extending our models to 3D, and anticipate that many findings will remain consistent.

Citation
Berrios-Rivera, N., Ozawa, S., & Dunham, E. M. (2025, 09). Elastic stress transfer from seismic slip and fluid pressure diffusion as primary mechanisms controlling slip front expansion in fluid-driven swarm seismicity. Poster Presentation at 2025 SCEC Annual Meeting.

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