Acoustically derived ice-fracture velocity in central Arctic pack ice

Sounds radiated by fractures in Arctic ice (called acoustic events) are used to estimate fracture velocity. Both speed and orientation are obtained by measuring Doppler shifts induced by source motion. Data from the SIMI experiment of 1994 in the central Arctic are used in the frequency window 10 to 350 Hz. The estimation procedure assumes that each fracture propagates unilaterally, i.e., unidirectionally. Results for a population of 186 events show fracture propagation speed to be mostly subsonic, in the range 100 to 1100 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 indicates either the presence of distinct multiple fractures in each event, or of a single mechanism at different stages in its propagation.