HR: 0800h
AN: S31A-1038    [Abstracts]
TI: The Apparent Periodicity of Felt Reports in the Alaskan Earthquake Record
AU: * Hafner, L A
EM: Hafner@HWS.edu
AF: Department of Geoscience, Hobart and William Smith Colleges, 2381 Scandling Center, Geneva, NY 14456 United States
AU: McNutt, S R
EM: steve@giseis.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, P.O. Box 757320, Fairbanks, AK 99775 United States
AB: Felt reports for Alaskan earthquakes were found to be non-uniformly distributed throughout the year. With a predominantly tourist economy, the Alaskan population nearly triples in the summer months, possibly affecting the reporting of earthquakes in the historical record. Using published felt reports from the National Earthquake Information Center and the Alaska Earthquake Information Center, the percentage of events felt each month in central mainland Alaska were tabulated and compared between the summer and winter seasons. Earthquakes were selected from January 1, 1990 to October 31, 2002, from latitudes 58 to 70 degrees N and longitudes 140 to 160 degrees W, and depths 0 to 200 km. 408 events were felt out of a total of 695 that occurred. A number of parameters, including time of day, latitude, longitude, and magnitude, were additionally compared to specify possible limiting factors within each season. While a strong seasonal effect was not found in magnitude 4.0 ML events and greater, the months of May and June were consistently found to have the highest percentage of felt events with a steep drop occurring in the month of July. We ascribe this effect to the summer melting of the top layer of frozen ground to a depth of about 1.5 meters. Additionally, smaller events from magnitude 1.0 to 4.0 ML were also examined. 396 events were felt out of a total of 7,451 that occurred. We found that small earthquakes were felt, with a significant difference, more readily during summer months than in winter. This is likely an effect of the higher summer population of tourists and greater distribution of open businesses. Together these observations suggest that the historical Alaskan earthquake record is likely biased in favor of more frequent reporting of events occurring in summer months as opposed to winter.
DE: 7230 Seismicity and seismotectonics
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting