Acoustic T-phase directionality measuments using a towed line array

Abstract

The directionality of acoustic T-phase signals radiated from a series of shallow undersea earthquake in the South Fiji Basin has been determined using a linear hydrophone array. The array was towed in the vicinity of 24 S 176 W in the northern part of the basin at a depth of 300 m. The T-phase signal from each earthquake lasted for about 5 min, with a maximum level about 2.5 min after the arrival of the initialP -phase event. The T-phase signal directionality was determined by processing the array data using a time-delay beamformer. The first part of the signal arrived on a direct bearing between the earthquake source and the array, but the subsequent stronger components arrived from different directions significantly farther south of the source. A model based on ray path travel times suggests that the later components of the T-phase signal are radiated into the water via downslope propagation from ridges and seamounts. The intitial components are scattered into the sound channel by leakage from the P-phase signal relatively close to the array.