HR: 13:55h
AN: C43A-02    [Abstracts]
TI: An Analysis of Glacial Earthquakes
AU: * Tsai, V C
EM: vtsai@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Ekstrom, G
EM: ekstrom@seismology.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AB: In 2003, Ekström et al. reported on the detection and location of a new class of earthquakes that occur in glaciated regions. The events are characterized by their lack of high-frequency radiation and surface-wave radiation patterns incompatible with standard double-couple or moment-tensor mechanisms. Ekström et al. proposed that the events correspond to large and sudden sliding motion of glaciers. The vast majority of these "glacial earthquakes" occur in Greenland, with a few events occurring in Antarctica and Alaska. We have examined 153 events on Greenland that occurred from 1993 to 2004. All events are much better fit by a landslide (CSF) model than by the typical double-couple earthquake (CMT) model. Surface-wave waveform fits to the CSF model result in much more accurate locations than are possible using the original detection algorithm. After relocation, the events strongly cluster into seven distinct regions, all of which correspond to regions of very high ice flow and most of which are named ice streams. The seven regions are: Daugaard Jensen Glacier, Kangerdlugssuaq Glacier, Helheim Glacier, the southeast Greenland glaciers, Jakobshavn Isbrae, Rinks Isbrae, and the northwest Greenland glaciers. As an example of the degree of clustering, in the Kangerdlugssuaq Glacier region, 61 events cluster within a 60 by 60 km area. Given the remaining uncertainties in the locations, this suggests that all of these events are associated with the Kangerdlugssuaq Glacier. For each event, the landslide modeling yields a force direction and the twice-integrated force couple, which can be interpreted as the landslide mass multiplied by the distance traveled. All events have a force direction roughly parallel to the local ice-flow direction inferred from remote sensing (laser altimeter, InSAR, and radar) data by other authors. Some events, however, are better fit either with a force couple in the direction opposite to the expected one, or with two force couples. These apparently reversed or double sliding mechanisms may be a result of using a symmetric force couple to model events that have a more complex source time function. All events have twice-integrated force couples between 0.12 - 2.04 *10¹⁴ kg*m, corresponding to earthquakes of surface-wave magnitude between 4.6 and 5.1.
DE: 0720 Glaciers
DE: 0730 Ice streams
DE: 0774 Dynamics
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Cryosphere [C]
MN: Fall Meeting 2005