A Comparison of Seismic Event Detection with IASPEI and Earthworm Acquisition Systems at Alaskan Volcanoes

Since 1988, Alaska Volcano Observatory (AVO) has been continually monitoring seismicity at active volcanoes in Alaska (Dixon et al. , 2004). The AVO seismic network has grown from 27 stations on the Cook Inlet volcanoes (Augustine, Iliamna, Redoubt, and Spurr) to 160 stations on 27 volcanoes in 2004 (Figure 1). Each seismograph subnetwork on an individual volcano typically consists of five short-period vertical stations and one short-period three-component station surrounding the volcanic center at distances of 1 to 20 km. The configuration of each subnetwork varies depending on numerous factors such as local topography, available telemetry options, and the grouping of individual volcanic centers. Historically, the AVO seismic network has used short-period geophones and standard analog telemetry because of reliability, cost, and availability. As telemetry bandwidth has become more readily available, AVO has begun to deploy broadband seismometers and digital communications for telemetry (Murray et al. , 2002). The purpose of this study is to evaluate the changes in earthquake detection rates associated with the shift from the IASPEI (International Association of Seismology and Physics of the Earth's Interior) acquisition system (Lee et al. , 1988) to the Earthworm acquisition system (Johnson et al. , 1995) in early 2002. Understanding how the earthquake detection rates have changed in response to this switch is a necessary component of AVO's long-term seismic monitoring program. To compare the performance of the IASPEI and Earthworm systems we calculate the rate of locatable earthquakes, the magnitude of completeness ( Mc ), and the proportion of located low-frequency (LF) earthquakes to all located earthquakes for subnetworks at Mount Wrangell, the Katmai volcanic cluster, and Makushin Volcano (Figure 1) for representative times for both acquisition systems. In addition, we compare the overall false trigger rate (number of false triggers to located earthquakes) for each acquisition system. The …