David M. Farmer Yunbo Xie
Inst. of Ocean Sci., P. O. Box 6000, Sidney, BC V8L 4B2, Canada
Acoustic and seismic emissions provide useful information on the mechanical properties of sea ice and its response to stress. Two recent field studies carried out under the ONR Ice Mechanics initiative have provided opportunities for exploring this approach to remote sensing using both passive and active measurements. Passive sensing revealed significant spatial variability in the response of the ice to thermal stress. Detailed analysis of the acoustic signal in the water yields insight on the source mechanism, which included local uplift, subsequently verified by inspection of the fracture site. Flexural waves in the ice were anisotropically distributed with blocking by a nearby pressure ridge dominating the spatial variability. Variations in ice properties were also probed with artificial impacts on the ice surface, revealing significant variability in both shear and p-wave propagation. The influence of the pressure ridge was very marked in its attenuation of flexural waves, but significant modifications of shear and p-wave velocities were also measured. Finally, advantage was taken of an artificially induced fracture experiment conducted by Dempsey and Spencer in April 1993. Controlled fracturing was induced with a flat-jack leading to multiple acoustical and seismic emissions that were detected with a hydrophone array. Such measurements should provide a basis for comparison with models for the fracture of heterogeneous materials.