HR: 1340h
AN: GC13A-0935    [Abstracts]
TI: A Closer View of Glacial Earthquakes Around Jakobshavn Glacier, Greenland, Using a Portable Seismic Array
AU: * Rial, J A
EM: jar@email.unc.edu
AF: Wave Propagation laboratory, University of North Carolina, Mitchell Hall, CB#3315, Chapel Hill, nc 27599, United States
AU: Tang, C
EM: chuanhaitang@gmail.com
AF: Wave Propagation laboratory, University of North Carolina, Mitchell Hall, CB#3315, Chapel Hill, nc 27599, United States
AU: Steffen, K
EM: Konrad.steffen@colorado.edu
AF: Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Campus Box 216, Boulder, CO 80309, United States
AB: Project SMOGIS (Seismic Monitoring of Greenland's Ice Sheet) the deployment of an array of portable seismic sensors around Swiss Camp (69.5N, 49.5W), some 50 km North of Jakobshavn glacier's ice stream (Western Greenland), has so far resulted in the possibly unprecedented detection of long lasting (up to 40 min. long) seismic "rumblings" which can be described as sustained seismic wave radiation episodes. We detected at least 80 of these in the 180 days of recording (May-August, 2006/2007). We also detected a number of sharp and short (15-20 s. long) distinguishable seismic events with source characteristics consistent with double couple mechanisms that occur during every rumbling and are clearly associated with them. These bona-fide earthquakes show strong P and S-wave radiation with amplitudes normally greater than the background rumbling, and are located around the margins of the ice stream that feeds Jakobshavn, some 50km south of the SMOGIS array. An important characteristic of the rumblings is that they are all very similar, despite their different durations, suggesting a fundamental similarity of process, a possibility that we are currently examining. A few rumblings were also detected by the global seismic network (GSN) and classified as glacial earthquakes, but the closer inspection allowed by SMOGIS reveals that they are more complex and intriguing than previously reported. Synthetic seismograms indicate that the focal mechanism of the double couple events is consistent with ENE oriented, nearly vertical fracture planes along which strike-slip motion with 20% vertical component takes place between the wedged ice and the graben's wall rock. Best fitting seismograms occur for a focal depth of ~2km below the surface of the ice stream. Since their occurrence seems controlled by the warm season, a long-term study of these rumblings should provide plausible upper limit for the ice volumes that outlet glaciers are able to drive into the ocean as the Arctic continuous to warm due to increasing global emissions of greenhouse gases into the atmosphere.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1621 Cryospheric change (0776)
DE: 1637 Regional climate change
DE: 4901 Abrupt/rapid climate change (1605)
DE: 8408 Volcano/climate interactions (1605, 3309)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting