Periodic Pore Fluid Pressure Perturbations as a Viable Mechanism for the Generation of Slow Slip Events on Velocity-Strengthening Faults

In recent years, geophysical observations have inferred temporal pore pressure changes that correlate with the occurrence of slow slip events (SSEs) in Hikurangi, Cascadia and central Japan subduction zones (Warren-Smith et al. 2019, Gosselin et al. 2020, Nakajima et al. 2018). These fluctuations in pore fluid pressure are interpreted as due to fluid migration during and between SSE cycles, which could be promoted by permeability changes during SSEs slip. These new observations raise important questions regarding the role of temporal variations in pore fluid pressure on the generation of SSEs. To examine these questions, here we study the effect of periodic perturbations of pore fluid pressure on a velocity-strengthening (VS) rate-and-state fault. We find that SSEs can be triggered by pore pressure changes under a wide range of VS conditions. The properties of the triggered SSEs depend on the relative magnitude (with respect to the background pore fluid pressure), duration, periodicity and size of the perturbation, as well as on the rate-and-state parameters. Remarkably, a model assuming periodic pore fluid pressure changes of a few MPa reproduces the properties (i.e. duration, slip, recurrence interval) of shallow SSEs observed along the central portion of the Hikurangi margin. In addition, our results indicate that these SSEs could be distinguished from spontaneous SSEs of comparable characteristics on VW faults by the temporal evolution of SSEs slip, as slip accumulates faster for the triggered SSEs. Our results suggest that a VS fault with periodic perturbations of pore fluid pressure is a viable mechanism for the generation of SSEs, which implies that the conditions that lead to SSEs within the rate-and-state framework are broader than previously thought.