HR: 0800h
AN: V21C-0614    [Abstracts]
TI: Repeating Long-Period Earthquakes at Shishaldin Volcano, Alaska
AU: * Petersen, T
EM: tanja@giseis.alaska.edu
AF: Alaska Volcano Observatory, Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Dr., Fairbanks, AK 99775-7320 United States
AU: McNutt, S R
EM: steve@giseis.alaska.edu
AF: Alaska Volcano Observatory, Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Dr., Fairbanks, AK 99775-7320 United States
AB: Since it last erupted in 1999, Shishaldin Volcano, Aleutian Islands, Alaska, has exhibited sustained seismicity consisting of many hundreds to ~2000 long-period (LP; 1--2Hz) events per day. Among these events many appear to have highly similar waveforms indicating repetitive and non-destructive source mechanisms. The events must occur within a very limited source volume (radius ≤ 500 m) in order to share such similar characteristics. We have applied waveform cross-correlation techniques to identify and extract a suite of repeating events (also commonly referred to as multiplets). A high correlation coefficient of ≥q 0.75 over an 8 sec window between individual earthquake signals is used to classify these events into a number of waveform families. The families, which are segregated by waveform differences reflecting subtle differences in locations and processes, also tend to be temporally separated from one another. These clusters of repeating events dominate Shishaldin's activity for several days up to several months at a time. Determining the location of LP earthquakes at Shishaldin has proven extremely difficult due to low signal-to-noise ratios and emergent waveforms. In order to analyze the spatial variation between different families we align waveforms within each cluster by using cross-correlation methods and then stack repeating events for the individual network stations. The improved signal-to-noise ratios allow P-wave arrivals to be identified. The standard earthquake location algorithm HYPOELLIPSE is used to calculate hypocentral locations for individual clusters. This method has been applied to a series of LP earthquake swarms. Improved locations utilizing the waveform families have been obtained. The clusters are located directly beneath the summit region. The source depth of the LP events is poorly resolved due to the lack of clear S-waves. However, all available data indicate that the LP seismicity is very shallow and is linked to the strong and continuous degassing activity of the volcano.
DE: 7280 Volcano seismology (8419)
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005