Ultrasonic Velocity Investigations of Crystal Anisotropy in Deep Ice Cores from Antarctica

• Main Authors: Kohnen,Heinz, Gow,Anthony J
• Other Authors: COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
• Format: Text
• Language: English
• Published: 1979
• Subjects: Snow; Ice and Permafrost; *ANISOTROPY; *LAND ICE; MEASUREMENT; CRYSTAL STRUCTURE; CORES; ANTARCTIC REGIONS; ULTRASONIC RADIATION; Antarctic; Byrd; Byrd Station; Little America; Little America V; The Antarctic; Antarc*; Antarctica; Ice; Ice Sheet; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA071451; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA071451

Ice cores from Byrd Station and Little America V have been used to test an ultrasonic technique for evaluating crystal anisotropy in the Antarctic Ice Sheet. P-wave velocities measured parallel and perpendicular to the vertical axes of cores from the 2164-m-thick ice sheet at Byrd Station have yielded results in excellent agreement with the observed c-axis fabric profile and with the in-situ P-wave velocity profile measured parallel to the bore hole axis. Velocity differences in excess of 140 m/s for core samples from deeper than 1300 m attest to the strong single pole clustering of crystallographic c-axes about the vertical, especially in the zone from 1300-1800 m. Such oriented structure is compatible only with strong horizontal shearing in this zone. The existence in an ice sheet of widespread shearing several hundred meters above its bed raises serious questions as to the validity of current concepts of the flow of large ice masses that tend to gloss over or ignore crystal alignments of this magnitude.