HR: 11:20h
AN: S52B-05    [Abstracts]
TI: Seismological Detection and Analysis of Recent Landslides in Alaska and the Yukon
AU: * Ekström, G
EM: ekstrom@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Hansen, R A
EM: roger@giseis.alaska.edu
AF: Geophysical Institute University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, United States
AU: Pavlis, G L
EM: pavlis@indiana.edu
AF: Indiana University, Deptartment of Geological Sciences, 1001 East 10th Street, Bloomington, IN 47405, United States
AU: Lipovsky, P
EM: Panya.Lipovsky@gov.yk.ca
AF: Yukon Geological Survey, 2099 2nd Avenue, Whitehorse, YT Y1A1B5, Canada
AB: Large landslides and avalanches generate seismic waves that can be used to detect, locate, and constrain the dynamic processes active in the slides. We have detected and located several landslide events using the Global Seismographic Network (GSN) as a long-period array. The detected events have equivalent long-period magnitudes of about M=5, while local magnitudes for these events, where available, are 2--3 magnitude units smaller. Two of the largest detected landslides are the 2005 Mount Steller (M=5.2) and the 2007 Mount Steele (M=5.2) events, located in the Pacific Coast Range in southern Alaska and the southern Yukon, respectively. In contrast to the forces active in standard earthquakes, in which seismic waves are generated as a consequence of tectonic stress drop within the Earth, landslides excite seismic waves through the time-varying forces caused by the acceleration and deceleration of a sliding mass interacting with the Earth's surface. Both the Mount Steller and the Mount Steele events involved sliding volumes of tens of millions of cubic meters of debris, vertical drops of around 2000 meters and runouts of more than 5 km. We use seismograms from several local and regional seismometers, including records from the STEEP PASSCAL array at epicentral distances as short as 10 km, to model the sliding process. We parameterize the source as a point force acting on the Earth's surface and obtain its magnitude, strike, and dip as a function of time. We observe the initial, nearly vertical, unloading force as the rock detaches from the solid Earth, a downward impulse as the mass is diverted into a horizontal trajectory at the base of the steep mountain slope, and the horizontal force corresponding to the deceleration phase as friction brings the sliding mass to a halt. Both slides have total durations of approximately 100 seconds. We find good agreement between the force histories inferred from seismograms and simple forward calculations of the dynamics of the sliding mass based on local topography, friction, and conservation of momentum.
DE: 1810 Debris flow and landslides
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting