Response of a fluid-saturated fault gouge to frequency varied cyclic pore-pressure variations

Cyclic fluid injection for industrial purposes within fault zones are commonly imposed, since they are observed to stabilize induced seismicity, often inducing aseismic slip along fault surfaces, without immediate seismic energy release (Zang et al., 2018; Noël et al., 2019; Ji et al., 2021a, 2021b, 2022). Even though dynamic variations of effective normal stress on fault zones due to both natural and anthropogenic causes are common (Chen et al., 2024), the impact of the perturbations and their frequencies on fault strength is less explored (Savage and Marone, 2007; Ferdowsi et al., 2015; Noël et al., 2019). The frequency of pore-pressure changes are  expected to impose a characteristic timescale, controlling the crossover from a drained to an undrained response, which in turn will promote markedly different deformation modes and rates (Passelègue et al., 2018).

 

In this work we present results from a coupled hydromechanical-discrete element model that simulates the response of a pre-stressed, fully saturated fault, filled with a granular fault gouge, subject to cyclic pore-pressure variations across frequencies of three orders of magnitude. For lower frequencies we see nucleation-arrest-nucleation dynamics within the granular rupture and for higher frequency we observe cyclic creep, both driven by pore-pressure perturbations. Within the frequency parameter space we see a crossover of the slip modes as we increase frequency, lower frequencies show unstable failure, while higher frequencies show creep. Our results might account for a) fluid induced slip stability in cyclic injection scenarios (higher frequencies) and b) low-frequency dynamic triggering of earthquakes.