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. Issue 9 (31st August 2022)

• Record Type: Journal Article
• Authors: Heimisson, Elías Rafn; Liu, Shengduo; Lapusta, Nadia; Rudnicki, John
• Is Part Of: Journal of geophysical research. Volume 127:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-31
• Subjects: rate‐and‐state friction -- poroelasticity -- induced seismicity -- boundary integral method -- fluid‐fault interactions -- dilatancy; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024185
• Languages: English
• ISSNs: 2169-9313

Abstract

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. Plain Language Summary: Earthquakes occur on faults deep in the Earth's crust. At this depth, faults are surrounded by rock and water that fills up pores and fractures. This water affects how the rock responds to earthquakes or slip on faults. Water also plays an important role within the faults since it will decrease or increase the frictional resistance by pressurization or depressurization, respectively. A common cause of pressurization is by injection of fluid, for example, during carbon sequestration or waste‐water disposal. Here we develop an efficient method to simulate fault slip and earthquakes in a porous and fluid‐filled medium. This allows us to understand better the role of water in causing pressure changes that affect the earthquake processes, either in the host rock or within the fault. We compare our method to a previously studied experiment in which water was injected directly into a fault and slip was measured. In addition, we investigate the poroelastic properties of the host rock, which describe how fluids interact with the elastic rock surrounding the fault. The poroelastic properties of the host rock have not received much attention in prior studies. They can significantly influence if and when an earthquake occurs due to injection. Key Points: We present a novel spectral boundary‐integral method for friction and fracture problems in a 2D poroelastic solid We solve for fault slip with fully‐coupled injection and dilatancy on a rate‐and‐state fault We identify significant influence of bulk poroelastic properties and bulk diffusivity on fault stability during injection