Rupture and Afterslip Controlled by Spontaneous Local Fluid Flow in Crustal Rock

Abstract

Shear rupture and fault slip in crystalline rocks like granite produce large dilation, impacting the spatiotemporal evolution of fluid pressure in the crust during the seismic cycle. To explore how fluid pressure variations are coupled to rock deformation and fault slip, we conducted laboratory experiments under upper crustal conditions while monitoring acoustic emissions and in situ fluid pressure. Our results show two separate faulting stages: initial rupture propagation, associated with large dilatancy and stabilized by local fluid pressure drops, followed by sliding on the newly formed fault, promoted by local fluid pressure recharge from the fault walls. This latter stage had not been previously recognised and can be understood as fluid‐induced afterslip, co‐located with the main rupture patch. Upscaling our laboratory results to the natural scale, we expect that spontaneous fault zone recharge could be responsible for early afterslip in locally dilating regions of major crustal faults, independently from large‐scale fluid flow patterns.

Effects of Dilatant Hardening on Fault Stabilization and Structural Development

“…However, structural observations show the samples are undergoing the same processes of dilation, microcrack coalescence, and fracture localization that occurs during typical brittle failure, albeit at a slower rate. Overall, our findings agree with previous studies of low‐porosity crystalline rocks which show similar behaviors of fault stabilization as a result of high pore fluid pressure (Aben & Brantut, 2021, 2023; Brace & Martin, 1968; Brantut, 2020; French & Zhu, 2017; Martin, 1980). We posit that apparent frictional sliding reflects transient sliding of geometrically complex faults and not a dilatant hardening process, as evidenced by the lack of a stress drop over durations lasting minutes to hours.…”

“…Periods of constant strength over such long durations have not been observed in previous studies of dilatant hardening. However, it is possible that some of our shorter duration periods of apparent frictional sliding are analogous to the stable failure events identified by Aben and Brantut (2023).…”