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Published February 14, 2022 | Submitted
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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.

Additional Information

License: Attribution-NonCommercial-NoDerivatives 4.0 International. Version 1: Sat, 12 Feb 2022; Version 2: Mon, 8 Aug 2022. This study was supported by the Geophysics Option Postdoctoral Fellowship from the Division of Geological and Planetary Sciences at Caltech and ETH Postdoctoral fellowship (Project No. FEL-19 20-2) to E.R.H. The work was further supported by the NSF IUCRC Center for Geomechanics and Mitigation of Geohazards (projects GMG-4.1, GMG-4.2) to N.L. Data Availability Statement: No original data is presented in this study. The data used in regard to application to the (Guglielmi et al., 2015) field experiment was archived by Larochelle et al. (2021b): CatechDATA repository (https://data.caltech.edu/records/1891). The software implementation of the method described in this paper is available here https://doi.org/10.5281/zenodo.6010353 (see Heimisson, 2022).

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Additional details

Created:
August 20, 2023
Modified:
October 23, 2023