HR: 1340h
AN: G33B-1233    [Abstracts]
TI: Measuring Ice Mass Fluctuations in Southern Alaska and Evaluating the Potential Influence on Tectonic Earthquakes
AU: * Sauber, J
EM: jeanne@steller.nasa.gov
AF: Planetary Geodynamics Lab., NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Ruppert, N
EM: natasha@giseis.alaska.edu
AF: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, United States
AU: Muskett, R
EM: rmuskett@iarc.uaf.edu
AF: International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775, United States
AB: In southern Alaska between the Malaspina and Bering Glaciers large ice fluctuations occur directly above a shallow main thrust zone associated with subduction of the Pacific-Yakutat plate beneath continental Alaska. Recently the southern Alaskan glaciers have shown a tendency toward earlier glacier melt onset and longer ablation season resulting in increased glacier wastage. Although these glaciers are generally undergoing ice mass loss, the temporal and spatial pattern of surface elevation change is complex and many of the larger glaciers undergo quasi-periodic surges. We have used ICESat-derived elevations along with InSAR-derived digital elevation models (DEM), such as the SRTM-C,-X DEMs, to detect general patterns in ice elevation change for surfaces with variable slope and roughness with exact and near-repeat ICESat tracks. Rather than averaging over large regions or relying on crossovers, we exploited the potential of individual ICESat waveform returns to estimate glacier elevations and surface characteristics. Careful interpretation of the ICESat waveforms must take into account the potential effects of signal saturation, forward scattering due to clouds, and field of view shadowing on pulse shape and the resulting errors in elevation and relief measurements. We have used our ICESat minus ICESat and ICESat minus InSAR-derived DEM elevation change results, along with earlier ice change studies, to estimate ice load changes from 1988-2006 for the southern coastal Alaska glaciers between the Malaspina and Bering Glaciers. The ice load changes were input to finite element models to calculate displacement rates, incremental stresses, and change in the fault stability margin. In 2002-2006, for instance, the predicted displacement rates of the solid Earth due to average annual change in ice loads were up to 20 mm/yr for the vertical and 3 mm/yr for the horizontal. To empirically evaluate the influence of short-term ice fluctuations on fault stability, we compared the seismic rate from a reference background time period against other time periods with variable ice or tectonic change characteristics. For most months regional temperatures in 2002-2006 were warmer than the longer-term average monthly temperatures (1917-2006). We found that the frequency of small tectonic events (2.2 < M < 3.0) in the Icy Bay region increased significantly in the 2002- 2006 time interval relative to the reference time period of 1988-1992. After AEIC removed identified icequakes, the seismic rate change for other time periods (1993-1996, 1997-2001) relative to 1988-1992 was not statistically significant and the tectonic events did not show a seasonal dependence. However, we found that during 2002- 2006 more earthquakes occurred in the late summer and fall than during other seasons.
DE: 0720 Glaciers
DE: 1225 Global change from geodesy (1222, 1622, 1630, 1641, 1645, 4556)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 1621 Cryospheric change (0776)
DE: 1645 Solid Earth (1225)
SC: Geodesy [G]
MN: 2007 Fall Meeting