Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1 through December 31, 2003

The Alaska Volcano Observatory (AVO), a cooperative program of the U.S.
Geological Survey, the Geophysical Institute of the University of Alaska
Fairbanks, and the Alaska Division of Geological and Geophysical Surveys, has
maintained seismic monitoring networks at historically active volcanoes in
Alaska since 1988. The primary objectives of this program are the near real
time seismic monitoring of active, potentially hazardous, Alaskan volcanoes and
the investigation of seismic processes associated with active volcanism. This
catalog presents the calculated earthquake hypocenter and phase arrival data,
and changes in the seismic monitoring program for the period January 1 through
December 31, 2003.

The AVO seismograph network was used to monitor the seismic activity at
twenty-seven volcanoes within Alaska in 2003. These include Mount Wrangell,
Mount Spurr, Redoubt Volcano, Iliamna Volcano, Augustine Volcano, Katmai
volcanic cluster (Snowy Mountain, Mount Griggs, Mount Katmai, Novarupta,
Trident Volcano, Mount Mageik, Mount Martin), Aniakchak Crater, Mount
Veniaminof, Pavlof Volcano, Mount Dutton, Isanotski Peaks, Shishaldin Volcano,
Fisher Caldera, Westdahl Peak, Akutan Peak, Makushin Volcano, Okmok Caldera,
Great Sitkin Volcano, Kanaga Volcano, Tanaga Volcano, and Mount Gareloi.
Monitoring highlights in 2003 include: continuing elevated seismicity at Mount
Veniaminof in January-April (volcanic unrest began in August 2002),
volcanogenic seismic swarms at Shishaldin Volcano throughout the year, and
low-level tremor at Okmok Caldera throughout the year. Instrumentation and data
acquisition highlights in 2003 were the installation of subnetworks on Tanaga
and Gareloi Islands, the installation of broadband installations on Akutan
Volcano and Okmok Caldera, and the establishment of telemetry for the Okmok
Caldera subnetwork. AVO located 3911 earthquakes in 2003.

This catalog includes: (1) a description of instruments deployed in the field
and their locations; (2) a description of earthquake detection, recording,
analysis, and data archival systems; (3) a description of velocity models used
for earthquake locations; (4) a summary of earthquakes located in 2003; and (5)
an accompanying UNIX tar-file with a summary of earthquake origin times,
hypocenters, magnitudes, phase arrival times, and location quality statistics;
daily station usage statistics; and all HYPOELLIPSE files used to determine the
earthquake locations in 2003.

[Summary provided by the USGS.]