Characteristics of Slow Slip Events Explained by Rate-Strengthening Faults Subject to Periodic Pore Fluid Pressure Changes

Abstract

Geophysical observations suggest that temporal changes in pore fluid pressure correlate with slow slip events (SSEs) at some subduction zones, including the Hikurangi and Cascadia subduction zones. These fluctuations in pore fluid pressure are attributed to fluid migration before and during SSEs, which may modulate SSE occurrence. To examine the effect of pore fluid pressure changes on SSE generation, we develop numerical models in which periodic pore-pressure perturbations are applied to a stably sliding, rate-strengthening fault. By varying the physical characteristics of the pore-pressure perturbations (amplitude, characteristic length and period), we find models that reproduce shallow Hikurangi SSE properties (duration, magnitude, slip, recurrence) and SSE moments and durations from different subduction zones. The stress drops of modeled SSEs range from ∼20–120 kPa while the amplitudes of pore-pressure perturbations are several MPa, broadly consistent with those inferred from observations. Our results indicate that large permeability values of ∼10−14 to 10−10 m2 are needed to reproduce the observed SSE properties. Such high values could be due to transient and localized increases in fault zone permeability in the shear zone where SSEs occur. Our results suggest that SSEs may arise on faults in rate-strengthening frictional conditions subject to pore-pressure perturbations.