HR: 11:05h
AN: C12B-04    [Abstracts]
TI: New Insight into Ice Shelf Rift Propagation from Geodetic and Seismic Monitoring
AU: * Bassis, J N
EM: jbassis@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Fricker, H A
EM: hafricker@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Coleman, R
EM: Richard.Coleman@utas.edu.au
AF: University of Tasmania, Hobart Campus, Geography-Geology Building, Hobart, TAS 7001 Australia
AU: Minster, B
EM: jbminster@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093 United States
AB: Rifts in Antarctic ice shelves are large through-cutting fractures that penetrate the entire ice thickness. These rifts can grow to be hundreds of kilometers long, eventually forming the boundary from which large tabular bergs detach. Despite the important role that iceberg calving plays in the mass balance of the Antarctic ice sheet (icebergs account for up to two thirds of the mass loss), very little is known about the forces involved in their initiation and subsequent propagation. During the 2002-2003 and 2004-2005 seasons we jointly deployed arrays of GPS and seismometers around the tip of an actively propagating rift on the Amery Ice Shelf, East Antarctica. Our observations show strong clustering of seismicity along the rift axis, extending far ahead of where the rift tip is visible on the surface. We also find episodic swarms of seismicity accompanied by rapid rift widening, which we interpret as bursts of rift propagation. The locations of events during the seismic swarm show that during each burst, the rift propagated approximately 100-200 meters. Previous studies have shown no direct triggering of bursts of propagation by tides or winds. Serendipitously, during the 2004-5 our instruments were deployed one week before the magnitude 9.3 Sumatra earthquake. Not only is the earthquake clearly visible in our seismic records, but we also see the arrival of T-waves (acoustic waves which propagate through the ocean) as well as the tsunami triggered by the earthquake. This presents us with a novel opportunity to study the influence of both the earthquake and the tsunami on rift propagation. We present preliminary results showing that neither the earthquake nor the T-waves had any effect on propagation. However, one of the bursts occurs several hours after the tsunami arrives at the ice shelf, suggesting a possible connection and raising questions about the potential influence of large storms and swell on propagation.
DE: 0726 Ice sheets
DE: 0728 Ice shelves
DE: 0732 Icebergs
DE: 0774 Dynamics
DE: 0776 Glaciology (1621, 1827, 1863)
SC: Cryosphere [C]
MN: Fall Meeting 2005