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Seismic activity at Cascade volcanic centers is monitored by a composite network of seismic stations operated by several groups (fig.1). These groups include the Pacific Northwest Seismograph Network (PNSN), operated by the University of Washington in cooperation with several other entities (such as the University of Oregon), and the Northern California Seismic Network (NCSN), jointly operated by the U.S. Geological Survey (USGS) Earthquake Hazards Team in Menlo Park and the University of California Berkeley. Both groups receive funding from the USGS Volcano Hazards Program, the USGS Earthquake Hazards Program through the National Earthquake Hazards Reduction Program (NEHRP) and Advanced National Seismic System (ANSS) programs, the National Oceanic and Atmospheric Administration (NOAA) through the Cooperative Remote sEnsing Science and Technology (CREST) program for tsunami mitigation, and other sources. Waveform data is shared in real time between these networks and other groups (including the Cascades Volcano Observatory (CVO)) via the USGS Earthworm data acquisition system (Bittenbinder and others, 1994). The PNSN also uses this system to receive data from several Canadian stations operated by the Pacific Geoscience Centre in Sydney, British Columbia.
The PNSN/NCSN combined network has a total of 44 stations within 20 km of individual stratovolcanoes, and 66 within 40 km (fig.1). The vast majority of these are short-period, vertical-component stations that use analog telemetry. This number also includes four broadband seismometers (one each near Rainier, Hood, Newberry, and Shasta; most are CREST-funded sites), two short-period three-component seismometers (Three Sisters, Lassen Peak), and five ANSS- and CREST-funded strong-motion accelerometers (near Mount Baker, Mount Rainier, Mount Hood, Three Sisters, and Newberry Volcano; three of these are co located with broadband instruments). CVO currently receives real-time data from 50 of these stations.
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