Acoustically derived ice-fracture velocity in central Arctic pack ice

Sounds radiated by fractures in Arctic ice (called acoustic events) are use d to estimate fracture velocity. Both speed and orientation are obtained by measuring Doppler shifts induced by source motion. Data from the SIMI expe riment of 1994 in the central Arctic are used in the frequency window 10 to 350 Hz. The estimation procedure assumes that each fracture propagates uni laterally, i.e., unidirectionally. Results for a population of 186 events s how fracture propagation speed to be mostly subsonic, in the range 100 to 1 100 m/s, significantly lower than the Rayleigh wave speed (1700 m/s for sea ice) assumed in previous studies. The wide range of speeds observed indica tes either the presence of distinct multiple fractures in each event, or of a single mechanism at different stages in its propagation. (C) 2000 Acoust ical Society of America. [S0001-4966(00)00707-4].