Viscous strengthening followed by slip weakening during frictional melting of chert

Abstract

Pelagic chert is one of the major lithologies in accretionary complexes. Thus, frictional properties of chert at seismic slip rates are important for understanding of earthquake faulting in subduction zones. Here, we conducted high-velocity friction experiments on chert collected from the Jurassic accretionary complex in central Japan at a slip rate of 1.3 m/s and normal stresses of 5–13 MPa under room humidity conditions. The results show that initial slip weakening was followed by slip strengthening and subsequent second slip weakening toward a steady-state shear strength. Slip strengthening resulted from the formation of a silica-rich melt layer at lower melting temperatures than expected, which could be due to the presence of water in the illite-containing chert. The second slip weakening may be occurred due to a decrease in shear strain rate associated with the thickening of the melt layer.[Figure not available: see fulltext.]