Kinematic and seismic analysis of the breakup of the giant iceberg B15A at Cape Adare, Antarctica

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• Prof Seelye Martin (University of Washington)
• Tuesday 20 July 2010, 15:00-16:00
• DAMTP, room MR4.

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Satellite imagery reveals that the large iceberg B15A , measuring 120 km by 30 km, broke up while exiting the Ross Sea in October 2005. Bathymetric observations revealed that the principal agent of these breakups is a previously unknown 9 km long shoal with minimum depths of 215 m. Satellite imagery shows that B15A and other icebergs are driven into the shoal by coastal currents that converge over the narrow continental shelf. Because B15A was instrumented with a seismograph, GPS , and fluxgate compass, this provided a unique opportunity to establish the details of the iceberg kinematics that were not revealed by satellite imagery alone and to correlate seismic events observed both on the iceberg and in the far field during breakup. B15A fractured from multiple strikes against Davey Shoal and the adjacent Possession Islands; these strikes were driven by the combination of tidal currents and the coastal mean flow. The periods of iceberg‐sourced seismic radiation were correlated with the strikes. The iceberg‐ and land‐based seismic signals showed that the iceberg fracture, its sliding across the shoals, and the ice‐on‐ice stick‐slip contacts among the postbreakup iceberg fragments generated the strong chaotic and harmonic tremor episodes, some of which were observed at distances as far as the South Pole, where these signals propagated as seismically coupled hydroacoustic T phases.

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