ACCURATE AZIMUTH ESTIMATES FROM A LARGE-APERTURE HYDROPHONE ARRAY USING T-PHASE WAVE-FORMS

A simple method is described whereby station-to-source azimuths are es timated by fitting a plane wave to envelope functions of T-phases obse rved on a 5-element hydrophone array around Ascension Island, South At lantic Ocean. When applied to a data set of 55 earthquakes of known lo cation ranging between 2 and 45 degrees distance from Ascension Island , estimated aximuths have a standard deviation of 3.3 degrees from ref erence azimuths when 3 or more hydrophone elements are used. The stand ard deviation decreases to 1.8 degrees if T-phase data from all 5 hydr ophone elements are used. We also investigate variations in predicted errors for different array geometries and arrival azimuths. This simpl e method is amenable to automation and can easily be incorporated into a global monitoring system.