Compressive shear faults within arctic sea ice: Fracture on scales large and small

[ 1] We examined fracture features within arctic sea ice as revealed by Landsat-7 and RADARSAT imagery, by an aerial survey, and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression. Regardless of scale, which spans the range from kilometers to millimeters, the features look alike. They consist mainly of narrow lineaments that traverse the field of view, plus wing-like and comb-like secondary cracks. The lineaments occasionally intersect and generally exhibit either right-lateral or left-lateral relative movement, like strike-slip faults within Earth's crust. We term them brittle compressive shear faults. They form through the linking of en echelon arrays of deformation-induced secondary cracks. From an application of wing-crack and comb-crack mechanics, we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses. To account for the brittle behavior of the sea ice cover, we applied a recent model of the ductile-to-brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators. In identifying the nature of sea ice fracture features, we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation, via the operation of scale-independent mechanisms.