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