Slip weakening in rocks and analog materials at co-seismic slip rates

Abstract

Determination of co-seismic slip resistance in earth faults is critical for understanding the magnitude of shear-stress reduction and hence the near-fault acceleration that can occur during earthquakes. Also, knowledge of shear resistance dependency on slip velocity, slip distance, normal stress, and surface roughness is fundamental information for understanding earthquake physics and the energy released during such events. In the present study, plate-impact pressure-shear friction experiments are employed to investigate the frictional resistance in fine-grained Arkansas novaculite rock and an analog material (soda-lime glass), under relevant interfacial conditions. The results of the experiments indicate that a wide range of frictional slip conditions can exist during a single slip event. These conditions range from initial no-slip followed by slip weakening, strengthening, and seizure at the frictional interface. For the case of glass vs. glass experiments, the first slip-weakening, with μ in the range of 0.4–0.2, is understood to be most likely due to thermal-induced flash heating and incipient melting at asperity junctions, while the slip-strengthening, with μ in the range of 0.1–0.4, is understood to be a result of coalescence and solidification of local melt patches. For the case of the fine grain Arkansas Novaculite rocks a similar range of slip conditions is observed.