Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tf) in the presence of frictioninduced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tf at 10 kilometers in depth. Friction experiments on tonalite samples show that tf depends weakly on normal stress. Extrapolation of experimental data yields tf values consistent with the field estimates and well below the Byerlee strength. We conclude that friction-induced melts can lubricate faults at intermediate crustal depths.