Controls of Gouge Heterogeneity on Cyclic Reactivation of Fault-Valve Systems

Fault zones are inherently heterogeneous and exert significant impacts on fluid injection-induced activities. We conducted Low-velocity shear experiments on homogeneous (HM) and layered (LM) clay-quartz mixtures representing gouge heterogeneity under double direct-shear and constant fluid injection. Cyclic fault-valve is activated in LM faults when the clay content is ≥50%, while it is absent in HM faults. A segmental layer of low-permeability clay perpendicular to the flow direction acts as a fault-valve, causing cyclic build-up then dissipation in pore pressure, hence influencing the magnitude of shear stress drop and sliding distance associated with seismic magnitudes. Recovered seismic moments from individual fault-valve cycles are bounded by the maximum seismic moment $M_0^{\max }=\frac{c}{2\left(1-c\right)}G∆V^{\prime }$ when a pre-stress coefficient c ranges 90–99%. This study highlights the role of spatial distributions in pore pressure as controlled by gouge compositions and spatial heterogeneity on slip stability, and verifies the applicability of $M_0^{\max }-∆V^{\prime }$ relation to fault-valve systems.