A spectral boundary-integral method for faults and fractures in a
poroelastic solid: Simulations of a rate-and-state fault with dilatancy,
compaction, and fluid injection
Abstract
Fluid-fault interactions result in many two-way coupled processes across
a range of length scales, from the micron scale of the shear zone to the
kilometer scale of the slip patch. The scale separation and complex
coupling render fluid-fault interactions challenging to simulate, yet
they are key for our understanding of experimental data and induced
seismicity. Here we present spectral boundary-integral solutions for
in-plane interface sliding and opening in a poroelastic solid. We solve
for fault slip in the presence of rate-and-state frictional properties,
inelastic dilatancy, injection, and the coupling of a shear zone and a
diffusive poroelastic bulk. The shear localization zone is treated as
having a finite width and non-constant pore pressure, albeit with a
simplified mathematical representation. The dimension of the 2D plane
strain problem is reduced to a 1D problem resulting in increased
computational efficiency and incorporation of small-scale shear-zone
physics into the boundary conditions. We apply the method to data from a
fault injection experiment that has been previously studied with
modeling. We explore the influence of bulk poroelastic response, bulk
diffusivity in addition to inelastic dilatancy on fault slip during
injection. Dilatancy not only alters drastically the stability of fault
slip but also the nature of pore pressure evolution on the fault,
causing significant deviation from the standard square-root-of-time
diffusion. More surprisingly, varying the bulk’s poroelastic response
(by using different values of the undrained Poisson’s ratio) and bulk
hydraulic diffusivity can be as critical in determining rupture
stability as the inelastic dilatancy.