2aUW14. Acoustic T-phase directionality measuments using a towed line array.

Session: Tuesday Morning, December 3

Time: 11:26

Author: N. Ross Chapman
Location: School of Earth and Ocean Sci., Univ. of Victoria, Victoria, BC V8W 3P6, Canada
Author: Ralph Marrett
Location: Defence Sci. Establishment, Auckland, New Zealand


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 initial P-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.

ASA 132nd meeting - Hawaii, December 1996