Slip Behaviors on an Artificial Fault Surface with Engraved Topography in a Laboratory Stick-Slip Experiment: Insights on the Roles of Fault Roughness in Spatial and Temporal Seismic Distribution

Repeating earthquakes have been interpreted as repeated ruptures of small local asperitieson a fault plane. The roughness of fault surface affects the slip behaviors and seismic nucleation significantly. We designed a "stick-slip" experiment using a saw-cut cylindrical PMMAsample.Periodic parallel ridges were laser engraved on part of the fault surface of the footwall. The remaining area was smoothed by polishing. The fault surface of the hanging wall has two artificial patches. One patch was machined to match the smooth area on the fault surface of the foot wall. The other patch was machined to make local contacts with periodic ridges on the fault surface of the foot wall. The surface topography was quantitatively measured by profilometer. The sample was subjected to conventional triaxial loading at 10 MPa confiningpressure. The differential stress increased from 15 MPa to 20 MPa with a constant loading rate of 1/120MPa/sec. During the slow slip of the artificial engraved fault surface,acoustic emissions (AEs) were triggered and monitored by 16PZT sensors.These AEs, well separated in space and time,were clustered into two groups- those repeatedly nucleated on the rough area and a second group on the smooth area. The spatial and temporal behaviors of the AEs show the interplay between slips on the two areas with different roughness. This experiment shows that laboratory designed roughness can tune the spatial and temporal seismic distribution on a fault plane.