Competition between thermal pressurization and dilatant strengthening in laboratory ruptures

Résumé fourni par la source

In fluid-saturated faults, thermal pressurization (TP) is predicted to induce rapid weakening, whereas dilatant strengthening (DS) can counteract this process through pore‐space expansion. However, experimental constraints on their competition remain limited. Here, we investigate these processes using triaxial stick–slip experiments with direct on- and off-fault pore pressure (Pp) measurements on saturated, saw‐cut, thermally cracked Westerly granite under effective confining pressures of 30–60 MPa. Results reveal a systematic rupture transition from co-seismic Pp rise (TP-type) to Pp drop (DS-type) with increasing shear strain, accompanied by a fast–slow–fast slip sequence, with slip velocities differing by up to three orders of magnitude. An undrained, adiabatic TP model reproduces the measured Pp rise evolution during early-stage fast events and indicates progressive shear zone widening that reduces TP efficiency. With continued slip, increasing cumulative plastic porosity reflects enhanced dilatancy during DS-dominated sequences. Microstructural observations reveal gouge development and a near-fault damage zone, providing independent evidence for this structural evolution. This evolution modifies fault stiffness and explains the observed transition in slip behavior. Despite contrasting Pp responses, fracture energy scales similarly with slip for both TP- and DS-type events, suggesting comparable rupture energetics. Overall, this study provides direct experimental evidence of TP–DS transitions, demonstrating that TP governs early-stage weakening but diminishes as dilatancy progressively strengthens with shear zone widening and near-fault damage. These results highlight that fault structure and its evolution plays a key role in controlling rupture dynamics in natural faults.

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