11:00 〜 11:15
[SCG45-17] Fault-valving instability: A mechanism for slow slip events
Many lines of geophysical and geological evidence suggest cyclic changes of pore pressure that synchronize or at least modulate seismic cycles. Fault valving (e.g., Sibson, 1992), which occurs via enhancement and reduction of along-fault permeability, is one possible mechanism for this. Fault valving is thought to be relevant to slow slip events and tremor in subduction zones (e.g., Kita et al. 2021). In our study, we explore the coupled dynamics of rate-and-state friction, along-fault fluid flow, and permeability evolution. We assume that permeability decreases over time by healing and sealing of microcracks and increases with slip. Using linearized stability analysis, we show that steady sliding with a constant updip fluid flow is unstable to small perturbations even for velocity-strengthening faults if enough background fluid flow is present. We refer to this new instability as the “fault-valve instability”. We also perform 2D numerical simulations with spatially uniform properties that fully capture the nonlinearity in the governing equations. We show that slow slip events, in the form of slip pulses, propagate in the direction of fluid flow as a manifestation of the fault-valve instability. The peak slip rate is tens to hundreds times larger than the loading velocity over a wide range of parameters, which is consistent with observed properties of slow slip events. Unlike the conditional stability mechanism (Liu & Rice, 2007), the slip per event and recurrence interval in our model are not very sensitive to the effective normal stress and state evolution distance of rate-and-state friction. We further conduct earthquake sequence simulations on dipping faults considering depth-dependent frictional and hydrologic properties. We reproduce quasi-periodic slow slip events in the deeper extension of the seismogenic zone. We discuss our mechanism of slow slip events with available observations in the Cascadia megathrust.