Measuring seismic waves using a towed underwater acoustic array

Abstract

This paper discusses the possibility of detecting shear and interface (Scholte) wave effects in the ocean using a towed hydrophone array. The shear field will be evanescent in the water and so may only be detected near to the ocean bottom interface. A benefit of measuring the acoustic field with a towed array is that a Hankel transform can be used to construct the horizontal wavenumber spectrum. If a shear or interface wave is measured, then it will be visible in the horizontal spectrum. The possibility of detecting the shear field will be strongly dependent on the shear wave speed in the sediment and this will also affect the detection of the more difficult to detect Scholte wave, which travels at about 90 % the shear wave velocity. The Scholte wave has a circular polarization where the shear wave may be vertical, horizontal, or a combination of the two polarities and may not be detectable for all frequency and source depth configurations. [Work supported by ONR.]