Wear processes in rocks at slow to high slip rates

Frictional wear experiments are performed on diorite, granite and sandstone at sliding velocities of 0.004–0.27 m/s under normal stresses of 0.21–6.3 MPa using a rotary-shear apparatus, to establish velocity-dependent wear laws of rocks and to determine the partition of frictional work used for gouge generation. Power-laws between normal/shear stresses and steady-state wear rate, defined as (thickness of gouge formed)/(fault displacement), account for our data for diorite and granite at low velocities and most experimental data on wear of rocks reported in the literature. But an exponential law holds for wear of diorite at velocities greater than 0.11 m/s and its wear rate increases dramatically at seismic slip rates. A change from the power-law to the exponential law seems to be caused by frictional heating and thermal fracturing. Both power and exponential laws can describe data for granite. Sandstones exhibit complex wear behavior possibly due to development of shiny slickenside surface that suppresses wear. Our data for diorite indicate that, at the investigated normal stresses, only 0.004% of frictional work is consumed for gouge formation at velocities less than 0.11 m/s, but this fraction increases markedly with increasing velocity. Energy partition for gouge formation is not constant and changes with velocity during earthquakes.

► Power laws between stress and wear rate hold for most rock-wear data at low velocity.
► Exponential laws hold for wear of diorite at velocity greater than 0.11 m/s.
► A change from the power to exponential laws could be due to frictional heating.
► Energy partition for gouge formation varies with velocity during earthquakes.