HR: 1340h
AN: V33A-0673    [Abstracts]
TI: High Levels of Non-Eruptive Seismicity at Mount Gareloi Volcano, Alaska
AU: * Caplan-Auerbach, J
EM: jca@usgs.gov
AF: Alaska Volcano Observatory, USGS Alaska Science Center, 4200 University Dr., Anchorage, AK 99508 United States
AU: Prejean, S G
EM: sprejean@usgs.gov
AF: Alaska Volcano Observatory, USGS Alaska Science Center, 4200 University Dr., Anchorage, AK 99508 United States
AB: Since 2003 when a seismic network was installed on Mount Gareloi, a remote Aleutian stratovolcano ~150 km west of Adak, AK, hundreds to thousands of earthquakes have been recorded daily. Catalog locations show a wide scatter around the edifice at depths ranging from 0-10 km. Gareloi earthquakes are typically long-period, although volcano-tectonic and hybrid earthquakes also are observed. Unlike earthquakes observed at other volcanoes with high levels of seismicity, such as Shishaldin, AK and Mount St. Helens, WA, the time series of individual events are different at Gareloi and likely do not represent a repeating source. Source processes such as bubble bursts, dome growth or conduit oscillation may thereby be ruled out as the sole seismic source at Gareloi. We present a new velocity model and high-resolution relocations for Gareloi seismicity and discuss the possible source processes responsible for the wide variety of seismic events. Gareloi erupts alkali-rich basalt and basaltic andesite from two active peaks, the southernmost of which contains an active fumarole field. The last large eruption (ash plume > 7 km high) of Gareloi occurred in 1982, but several small tephra plumes were observed in the 1980's, with one unconfirmed plume described in 1996. Despite the exceptionally high level of seismicity recorded at Gareloi, other indicators of unrest, such as increased steaming or thermal anomalies in satellite data, have not been observed since the seismic network was installed. However, on September 2, 2005 a 70-minute period of volcanic tremor was recorded following a five day period of intense seismicity and could represent a small eruption. The amplitude of earthquakes at Gareloi declined immediately following the tremor, but the rate remained approximately the same, at ~1 earthquake per minute. This seismic sequence provides new insight into the potential source mechanisms associated with Gareloi seismicity and could allow us to better evaluate Gareloi's eruptive behavior.
DE: 7215 Earthquake source observations (1240)
DE: 7280 Volcano seismology (8419)
DE: 8419 Volcano monitoring (7280)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005