Seismic studies on Fletcher's Ice Island, T‐3

Abstract

Seismic studies were made on Fletcher's Ice Island in the Arctic Ocean fertng June and July, 1952, to determine the thickness and elastic characteristics of this ice body. Two types of seismic profiles were made, one using explosives detonated at or near the surface, and one using mechanical impacts. Compressional and torsional velocities were obtained, as well as good flexural waves at the longer distances. A single shot was fired at the surface at a distance of 5 ½ miles for the generation of an air‐ice coupled wave. In addition to these standard types, a constant frequency multi‐reflected SV wave showed unusually large amplitudes at the long distances. The ice thickness was obtained independently by seismic energy reflected from the ocean bottom. The arrival times through the island were compared with arrival times to the surrounding ice pack at sea level. The thicknesses obtained by these various types of measurement are quite consistent, giving from 160 to 170 ft, corresponding to an average density of about 0.91 gms/cm3, as deduced from the elevations. This value of density was also obtained by direct measurements in the upper 50 ft of ice.