Influence of Creep Compaction and Dilatancy on Earthquake Sequences and Slow Slip

Fluids influence fault zone strength and the occurrence of earthquakes, slow slip events, and aseismic slip. We introduce an earthquake sequence model with fault zone fluid transport, accounting for elastic, viscous, and plastic porosity evolution, with permeability having a power-law dependence on porosity. Fluids, sourced at a constant rate below the seismogenic zone, ascend along the fault. While the modeling is done for a vertical strike-slip fault with 2D antiplane shear deformation, the general behavior and processes are anticipated to apply also to subduction zones. The model produces large earthquakes in the seismogenic zone, whose recurrence interval is controlled in part by compaction-driven pressurization and weakening. The model also produces a complex sequence of slow slip events (SSEs) beneath the seismogenic zone. The SSEs are initiated by compaction-driven pressurization and weakening and stalled by dilatant suctions. Modeled SSE sequences include long-term events lasting from a few months to years and very rapid short-term events lasting for only a few days; slip is ∼1–10 cm. Despite ∼1–10 MPa pore pressure changes, porosity and permeability changes are small and hence fluid flux is relatively constant except in the immediate vicinity of slip fronts. This contrasts with alternative fault valving models that feature much larger changes in permeability from the evolution of pore connectivity. Our model demonstrates the important role that compaction and dilatancy have on fluid pressure and fault slip, with possible relevance to slow slip events in subduction zones and elsewhere.