Large-scale (100 km) rectilinear lead patterns are a common feature of the Arctic Ocean ice cover. We show that many of the characteristics of these patterns can be explained by analogy with rock mechanics. In particular, the existence of two intersecting lead sets, the typical intersection angles of 28¿, and the observed relative shearing motions are consistent with faulting associated with semibrittle failure. Further support for this explanation has been obtained by using NOAA and Landsat satellite imagery over an approximately 100-km-square area of the Beaufort Sea. These provide coverage of 2 days of ice deformation prior to the formation of a lead at 14¿ to the axis of compression. Strains of 47XX over the 2-day period are within the range attributed to rock distortion preceding semibrittle failure. Finally, we suggest that the range from brittle to plastic type behavior is feasible within the Arctic Ocean sea ice, depending upon the applied rate of strain and/or the ambient confining pressures.