Shear faulting and localized heating in ice: The influence of confinement

Systematic experiments on laboratory-grown polycrystalline granular ice and columnar S2 ice loaded triaxially at −10 °C at a strain rate ε˙11=2.2×10-2s-1 under increasing levels of confinement have established two distinct modes of brittle-like shear faulting. One mode, termed Coulombic (C) or frictional faulting, develops under lower degrees of confinement and is characterized by macroscopic faults, comprising a narrow band of microcracks, oriented ∼30° from the direction of maximum shortening; and by pressure hardening, grain-size-dependent strength, localized heat production and the creation of fault gouge. The second mode of faulting, termed plastic (P) or non-frictional faulting, develops under higher degrees of confinement and is characterized by macroscopic faults, comprising a fine band of recrystallized grains, oriented ∼ 45° to the direction of maximum shortening; and by pressure and grain-size-independent strength and localized heat production. The transition from C-faulting to P-faulting corresponds to the level of confinement required to suppress frictional sliding.