In support of the proposed Comprehensive Nuclear Test Ban Treaty, a large database of hydrophone recordings including T-phases, explosions, and noise has been compiled and cross referenced with known seismic events at the Center for Monitoring Research. Using this database, an automated hydroacoustic arrival detection and classification system has been developed. Detection is accomplished with a long-term-average/short-term-average power detector operating in several passbands. Station specific tuning of SNR thresholds and passband bounds allows the detector to trigger reliably on T-phases and explosions while passing over the majority of noise events such as whale calls. For each detected arrival, features such as duration, energy moments, spectral ratio, and order statistics are measured in multiple passbands from 2–85 Hz. A neural network uses these features to classify each arrival as signal or noise. Declared signals are passed to a second-stage network which classifies them as T-phases, explosions, or unknown events. T-phases arriving within a 4-min window around the time predicted from a seismic location are associated with that seismic event. These associations reveal relationships among event parameters such as location, magnitude, depth, duration, and coupling region.

The rolling text of Conference on Disarmament’s Nuclear Test Ban Treaty requires monitoring by 169 seismic, 11 hydroacoustic, 60 infrasonic, and 50 radionuclide stations. Stations will continuously transmit data to a center for real-time processing. Processing will detect, measure, and classify signals, then it will associate signals at different stations and locate sources. Results will be reviewed by analysis. To prepare, the Center for Monitoring Research participates in a seismic monitoring experiment, which is being broadened to other technologies. Continuous data from hydrophones at Point Sur and Wake Island have been received and processed at CMR since late 1995. Data from additional hydroacoustic stations are imminent. Software for processing seismic data will be adapted for hydroacoustics; real-time detection and feature measurement are underway. Visual review found signals from 30% of shallow, Pacific-region seismic sources in CMR’s bulletin, but the rate varied widely by source region. Among mb≳4.2, h<100 km earthquakes, detection was independent of magnitude and earthquake depth. Ocean depth near the epicenter may control hydroacoustic detection. Differences between visually selected onset times and times predicted from seismic locations and propagation modeling vary widely by region, and are often larger than differences predicted from seismic location uncertainty.