Poster Presentation

How faults build up stress from the prior earthquake is vital for the seismic cycle. While the majority of fault shear stress recovery occurs during interseismic periods, little attention has been paid to the coseismic fault shear stress recovery. Additionally, even though dynamic fault weakening is critical for earthquake initiation and has been extensively studied, dynamic fault re-strengthening has rarely been investigated. Our previous work showed consistent coseismic fault weakening and shear stress recovery in high-speed friction tests. This work focuses specifically on coseismic shear stress recovery via three different types of laboratory stick-slip experiments: double direct shear, rotary shear, and triaxial shear tests. Besides mechanical data analysis, we are exploring the micro-mechanisms via IR thermographs, profilometry, and electron microscopy. Experiments on ~m/s direct shear and stick-slips show considerable coseismic shear stress recovery of more than 30% for granitic faults. The friction-velocity relation for the strengthening period obeys the ∞ 1/V trend, favoring the flash-weakening mechanism. Preliminary observations of IR thermography showed limited background temperature rise during stick-slips at the sub-mm scale. However, SEM images confirmed consistent gouge sintering and melting. This work will contribute to a better understanding of fault and earthquake mechanics, including better characterizing the rate-dependence of coseismic faulting and the constitutive friction relation, exploring the effect of different fault geometry, loading style, and material stiffness on dynamic faulting and friction evolution, and investigating fault re-strengthening mechanisms, energy dissipation, and interseismic stress build-up processes.