Flash weakening is limited by granular dynamics

We measured the steady-state friction coefficient of granite over a wide range of sliding velocities and pressures. We observed considerable weakening, described well by a flash-heating theory, above the sliding velocity of 1 cm/s regardless of pressure. At higher velocities, the velocity strengthening behavior replaced the velocity weakening behavior. This strengthening at higher velocities agrees with data from numerical simulations on sheared granular matter and is therefore described in terms of energy dissipation due to the inelastic deformation of grains. We propose a unified steady-state friction law that well describes the velocity and pressure dependence of the steady-state friction coefficient. Citation: Kuwano, O., and T. Hatano (2011), Flash weakening is limited by granular dynamics, Geophys. Res. Lett., 38, L17305, doi:10.1029/2011GL048530.