Monitoring Pacific Ocean seismicity from an autonomous hydrophone array

Since May 1996, an array of autonomous hydrophone moorings has been continu ously deployed in the eastern equatorial Pacific to provide long-term monit oring of seismic activity, including low-level volcanic signals, along the East Pacific Rise between 20 degreesN and 20 degreesS and the Galapagos Rid ge. The instruments and moorings were designed to continuously record low-f requency acoustic energy in the SOFAR channel for extended periods and prod uce results comparable to those previously derived by using the U,S. Navy S ound Surveillance SS stem (SOSUS) The technology and methodology developed for this in the northeast Pacific. The technology and methodology developed for this experiment, including instrument design, mooring configuration, a nalysis software, location algorithms (with an analysis of errors), and a p redicted error field, are described in detail. Volcanic activity is observe d throughout the Pacific, along with seismicity along transform faults, sub duction zones, and intraplate regions. Comparison data sets indicate detect ion thresholds and accuracy better than the land networks for open ocean ar eas and results comparable to. or better than, SOSUS, Volcanic seismicity a long the fast spreading East Pacific Rise appears similar in the Northeast Pacific but with much shorter durations. to documented examples In One exam ple from the intermediate spreading Galapagos Ridge is comparable to northe ast Pacific examples? and several episodes of activity were observed in the Wilkes Transform Fault Zone. A site of continuing off-axis seismicity is l ocated near 18 degreesS and 116 degreesW. Isolated intraplate earthquakes a re observed throughout the study area. Earthquake information from this exp eriment and future observations will be provided through the World Wide Web and earthquake data centers.