HR: 1340h
AN: V53D-1601    [Abstracts]
TI: Very-long-period seismic source at Mount St. Helens
AU: * Waite, G P
EM: gwaite@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS-910, Menlo Park, CA 94025 United States
AU: Chouet, B
EM: chouet@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS-910, Menlo Park, CA 94025 United States
AU: Dawson, P
EM: dawson@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS-910, Menlo Park, CA 94025 United States
AU: Moran, S C
EM: smoran@usgs.gov
AF: U.S. Geological Survey, Cascades Volcano Observatory, 1300 SE Cardinal Ct., Vancouver, WA 98683 United States
AB: We present preliminary analysis of very-long-period signals associated with the current eruption at Mount St. Helens. The eruption began in October 2004 and has continued building a lava dome to the present. Small (M<2), shallow (<1 km below the crater), repetitive earthquakes have occurred since the beginning of the eruption. A temporary network of 19 broadband seismographs (18 with 30 s Güralp CMG-40T and 1 with a 120 s Streckeisen STS-2) was installed in June 2005 to augment the permanent monitoring network and investigate these earthquakes. Together with a permanent broadband seismograph (with a 30 s Güralp CMG-6TD), we have broadband data from 20 stations within 6 km of the active vent. These data show that very-long-period (25 s) events generally accompany the shallow earthquakes. Similarity among VLP waveforms from different events reflects the repetitive action of a non-destructive source. The VLP energy is generally too weak to be detected by more than the two closest stations, but several larger earthquakes (M>2.5) have much more associated VLP energy that is observable on stations 6 km from the crater. Particle motions indicate the VLP source is near the center of the crater and very shallow. We are conducting a quantitative analysis of representative VLP events by moment tensor inversion of the waveform data. Preliminary results of this analysis will be presented.
DE: 7280 Volcano seismology (8419)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005