Abstract

Aseismic slip may occur during a long preparatory phase preceding earthquakes, and what controls it remains poorly understood. In this study, we explored the potential dependencies of the slow slip during the preparatory stage prior to stick-slip instabilities on two main factors, namely the loading rate and surface roughness. To that end, we conducted shear stress-driven friction experiments by imposing varying loading rates on sawcut granite samples with different surface roughness at confining pressure of 35 MPa. We measured the average slip along the fault using far-field displacements and strain changes, while using acoustic emission sensors and local strain gages to capture local slip variations. We found that the average aseismic slip during preparatory stage increases with roughness, whereas its duration decreases with increased loading rate. These results also evidence a complex slip pattern on rough faults which leads to dynamic ruptures at high loading rates.