Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1,1994 through December 31, 1999; USGS

Between 1994 and 1999, the Alaska Volcano Observatory (AVO) seismic monitoring
program underwent significant changes with networks added at new volcanoes
during each summer from 1995 through 1999. The existing network at Katmai
?Valley of Ten Thousand Smokes (VTTS) was repaired in 1995, and new networks
were installed at Makushin (1996), Akutan (1996), Pavlof (1996), Katmai - south
(1996), Aniakchak (1997), Shishaldin (1997), Katmai - north (1998), Westdahl,
(1998), Great Sitkin (1999) and Kanaga (1999). These networks added to AVO's
existing seismograph networks in the Cook Inlet area and increased the number
of AVO seismograph stations from 46 sites and 57 components in 1994 to 121
sites and 155 components in 1999. The 1995?1999 seismic network expansion
increased the number of volcanoes monitored in real-time from 4 to 22,
including Mount Spurr, Redoubt Volcano, Iliamna Volcano, Augustine Volcano,
Mount Snowy, Mount Griggs, Mount Katmai, Novarupta, Trident Volcano, Mount
Mageik, Mount Martin, Aniakchak Crater, Pavlof Volcano, Mount Dutton, Isanotski
volcano, Shisaldin Volcano, Fisher Caldera, Westdahl volcano, Akutan volcano,
Makushin Volcano, Great Sitkin volcano, and Kanaga Volcano (see Figures 1-15).
The network expansion also increased the number of earthquakes located from
about 600 per year in 1994 and 1995 to about 3000 per year between 1997 and
1999.

Highlights of the catalog period include: 1) a large volcanogenic seismic swarm
at Akutan volcano in March and April 1996 (Lu and others, 2000); 2) an eruption
at Pavlof Volcano in fall 1996 (Garces and others, 2000; McNutt and others,
2000); 3) an earthquake swarm at Iliamna volcano between September and December
1996; 4) an earthquake swarm at Mount Mageik in October 1996 (Jolly and McNutt,
1999); 5) an earthquake swarm located at shallow depth near Strandline Lake; 6)
a strong swarm of earthquakes near Becharof Lake; 7) precursory seismicity and
an eruption at Shishaldin Volcano in April 1999 that included a 5.2 ML
earthquake and aftershock sequence (Moran and others, in press; Thompson and
others, in press). The 1996 calendar year is also notable as the seismicity
rate was very high, especially in the fall when 3 separate areas (Strandline
Lake, Iliamna Volcano, and several of the Katmai volcanoes) experienced high
rates of located earthquakes.

This catalog covers the period from January 1, 1994, through December 31,1999,
and includes: 1) earthquake origin times, hypocenters, and magnitudes with
summary statistics describing the earthquake location quality; 2) a description
of instruments deployed in the field and their locations and magnifications; 3)
a description of earthquake detection, recording, analysis, and data archival;
4) velocity models used for earthquake locations; 5) phase arrival times
recorded at individual stations; and 6) a summary of daily station usage from
throughout the report period. We have made calculated hypocenters, station
locations, system magnifications, velocity models, and phase arrival
information available for download via computer network as a compressed Unix

tar file.