HR: 1330h
AN: S52C-0154    [PDF]
TI: Seismic Monitoring of Alaska's Volcanoes: A Comparison of Event Detection With IASPEI and Earthworm Acquisition Systems
AU: * Dixon, J P
EM: jpdixon@usgs.gov
AF: U. S. Geological Survey, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Power, J A
EM: jpower@usgs.gov
AF: U. S. Geological Survey, 4200 University Drive, Anchorage, AK 99508 United States
AU: Stihler, S D
EM: scott@giseis.alaska.edu
AF: University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AB: The Alaska Volcano Observatory (AVO) currently operates 140 seismic stations that are used to monitor 24 active volcanoes in Alaska. Each volcano generally has 6 to 10 short-period stations within 25 km of the summit. From October 1989 through February 2002, seismic events were detected and digitally recorded using an IASPEI acquisition system. In March 2002, the IASPEI system was replaced by an Earthworm acquisition system running in event detection and continuous modes. We have compared seismicity rates, magnitude of completeness and the proportion of low frequency to volcano-tectonic (VT) events detected at Mount Wrangell, Makushin Volcano, and the Katmai volcanic cluster for representative time periods using both acquisition systems. These volcanoes were chosen because each had minimal station outages, significant seismicity with no eruptive activity, and represented different tectonic regimes. The comparison indicates that the Earthworm system detects more events and a greater number of low frequency events than the IASPEI system. With the increase in detected events, a corresponding decrease in false triggers was also observed. For Wrangell there was an increase in the proportion of low frequency events detected (90.9% to 98.9%) and a decrease in magnitude of completeness from 1.8 to 0.9. For the Katmai volcanic cluster the proportion of low frequency events detected (3.8% to 1.4%) and the magnitude of completeness (0.8 to 0.7) both declined. At Makushin, the proportion of low frequency events detected increased slightly (6.4% to 7.7%) and the magnitude of completeness dropped from 1.4 to 1.0. Further, the magnitude of completeness for all 24 monitored volcanoes either declined or remained constant with the introduction of the Earthworm system, resulting in a greater total number of detected events. The increased numbers of detected VT earthquakes and low frequency events allow for more accurate assessments of the seismicity of Alaskan volcanoes.
DE: 7280 Volcano seismology (8419)
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting