Oral Presentation

Slip on faults induces compression and dilation in the surrounding rock, which can interact with pore fluids, modify their pressure, and induce fluid flow; those fluid effects, in turn, modify fault shear resistance and affect the slip evolution. The poroelastic coupling of slip and pore fluids is often ignored in modeling of seismic and aseismic slip, although several studies that considered the coupling using poroelasticity found that it can affect the fault slip in qualitative ways (Dunham and Rice, JGR, 2008; Heimisson et al., JMPS, 2019). Furthermore, fault slip induces dilatancy and compaction of the fault gouge, and the resulting pore space change can also lead to significant changes in pore fluid pressure and hence fault shear resistance and slip patterns (Segall and Rice, JGR, 1995; Segall et al., JGR, 2010; Dal Zilio et al., GRL, 2020).

We study the effects of poroelastic coupling and dilatancy, and their combination, using an example of a 1D fault that experiences fluid injection and a novel spectral boundary-integral approach for quasi-dynamic simulations of slip on a fault embedded into a fluid-saturated and diffusive poroelastic bulk (Heimisson et al., JGR, 2022). We find, surprisingly, that poroelastic properties of the bulk, which are rarely explored in modeling of fault slip, can qualitatively affect rupture stability and propagation. Further, we find that the stabilization by bulk diffusion and poroelastic properties can be comparable to that of dilatancy, a well-known stabilizing mechanism. We find that dilatancy can strongly alter the pore pressure distribution on the fault as slip evolves which, if measured in field experiments, would help constrain hydrological and mechanical properties of the fault and bulk. Our future modeling will explore additional fluid effects, such as the evolution of permeability with dilatancy and potential pressurization of pore fluids due to shear heating.

Our study highlights the need to consider coupled and dynamically evolving fluid effects in modeling fault slip, as well as the importance of determining realistic fault zone properties related to poroelasticity and dilatancy.