Sliding along Coulombic shear faults in ice

Abstract

New experiments have been performed on the resistance to inelastic deformation through frictional sliding along naturally-formed Coulombic shear faults in ice Ih. Coulombic faults mark terminal failure of virgin material when loaded rapidly under a moderate degree of confinement. The experiments were performed on S2 fresh-water ice at –10°C, proportionally loaded biaxially across the columns along a variety of all-compressive paths. Two kinds of behavior were observed. At higher sliding velocities (8 × 10–2 and 8 × 10–1 mm s–1) sliding was noisy and the process exhibited velocity weakening. At a lower sliding velocity (8 × 10–4 mm s–1) sliding was quiet and fault healing occurred. The two kinds of sliding are indicative of brittle-like (at higher speeds) and ductile-like (at lower speeds) behavior, and are explained in terms of fracture and creep. Within the brittle regime, a power law describes the relationship between the shear strength of the fault and the normal stress across it at the onset of sliding, while Coulomb's law describes the relationship once sliding has progressed by about 2 mm. PACS No.: 61.72Nn