Abstract
Drastic grain comminution is frequently observed in upper-crust faults
and large rock avalanche deposits. Here we report our model experiments
to elucidate the possible role of grain comminution in dry granular
friction. We sheared halite (NaCl) grains with a ring-shear
configuration at a constant slip rate under various normal stresses and
investigated the post-slip structures of the experimental fault zones
using micro X-ray computed tomography. Consequently, distinct frictional
behaviors were observed: a constant friction regime at small slip
displacements and a frictional weakening regime at large displacements.
The characteristic slip lengths for the two regimes decreased with
increasing normal stress and were characterized by approximately the
same exponent, regardless of the initial grain size. We developed a
theoretical model that considered the production, saturation, and
overflow of fine particles in the shear zone and successfully reproduced
the transient frictional behavior in the experiments.