Lithology and Stiffness Controls on Coseismic Fault Weakening and Re-Strengthening in Stick-Slip Friction Experiments

Xiaofeng Chen

Submitted August 30, 2026, SCEC Contribution #15529, 2026 SCEC Annual Meeting Poster #006

Earthquake cycles are governed by the accumulation and release of tectonic stress. Stress accumulates on locked faults during interseismic periods and is released rapidly during earthquakes. Consequently, most studies have focused on coseismic stress drop, or dynamic fault weakening, because of its direct role in earthquake initiation. In contrast, although laboratory experiments have reported dynamic fault restrengthening as slip velocity decreases toward arrest, its characteristics and underlying mechanisms remain poorly understood. Here, I present stick-slip friction experiments using a double-direct-shear apparatus on Westerly granite and Sioux quartzite under normal stresses of 3–24 MPa and loading rates up to 1 mm/s. High-resolution stress and displacement measurements (25 kHz) captured the complete evolution of stress and slip velocity during stick-slip events, revealing consistent coseismic restrengthening following the initial stress drop. Stress drops range from <0.01 to 4.6 MPa, while peak velocities range from 2 mm/s to 0.63 m/s. For both lithologies, the friction–velocity relationship at peak velocity agrees with flash-heating predictions, with Westerly granite consistently exhibiting higher friction than Sioux quartzite. The two lithologies exhibit contrasting restrengthening behavior. Westerly granite consistently recovers 50–80% of the initial stress drop, whereas Sioux quartzite shows highly variable recovery of 2–60%. Breakdown work scales with slip at the initial stress drop, whereas total stress drop scales linearly with total coseismic slip. These results indicate that the initial stress drop reflects a common rupture initiation process, whereas subsequent coseismic restrengthening is governed by lithology and loading-system stiffness, which together regulate overall coseismic stress release.

Key Words
Coseismic strengthening, stress drop, stick-slips

Citation
Chen, X. (2026, 08). Lithology and Stiffness Controls on Coseismic Fault Weakening and Re-Strengthening in Stick-Slip Friction Experiments. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)