The objectives of this investigation were as follows: to determine and study those characteristics of the sea floor that affect the propagation of sound and the predictions of low-frequency surveillance-system performance; to support specific underwater acoustic experiments in the northwestern Indian Ocean during the BEARING STAKE exercise by furnishing information on acoustic and related properties of sediment and rock layers in the form of geoacoustic models of the sea floor; and to produce additional geoacoustic models of the sea floor to allow extrapolation of the results of the bottom-loss experiments into adjacent areas.
The general objectives of this investigation were to determine and study those characteristics of the sea floor that affect sound propagation and the prediction of sonar performance; to support underwater acoustics' experiments and theory by furnishing information on the mass physical properties of sediments and rocks in the form of geoacoustic models of the sea floor; and to develop models of the sea floor which include gradients of sound velocity and attenuation, density, and elastic properties. Specifically, the minor objectives were to revise and review earlier work on the relations between frequency and attenuation of compressional (sound) waves in marine sediments and on the relations between attenuation and sediment porosity. The major objectives were to determine and predict variations of the attenuation of sound waves with depth in the sea floor.
The information and technology necessary to derive a valid geological-geophysical-acoustic model of the sea floor are presented. Two contrasting models are detailed and discussed: one in the Bering Sea which has a shallow-water, high-velocity, hard-sand bottom; and the Mohole (Guadalupe Site) model which has a deep-water, low-velocity, soft-clay bottom. Other models are to be reported in a continuing series. (Author).
The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet. The papers range from high resolution, holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic.
vi These categories seem to represent the basic breakdown by field of present-day research in this area. Though each paper has been classified into one of these categories (for conference organization purpose), many papers overlapped two or three areas. It is also interesting to note that not only are scientific results being communicated, but the latest techniques and the state-of-the-art tools of the trade (existing and in development) are also being presented. The forty-six papers presented at this conference represent the work of seventy scientists working at universities, government laboratories, and industrial laboratories in seven different countries . We would like to thank the contributors for their efforts and especially for their promptness in providing the editors with their final manuscripts. William A. Kuperman Finn B. Jensen La Spezia, Italy July 1980 CONTENTS GEOACOUSTIC PROPERTIES OF MARINE SEDIMENTS Attenuation of Sound in Marine Sediments . • 1 J. M. Hovem Directivity and Radiation Impedance of a Transducer 15 Embedded in a Lossy Medium . •• •••••• G. H. Ziehm Elastic Properties Related to Depth of Burial, Strontium Content and Age, and Diagenetic Stage in Pelagic Carbonate Sediments . . • • . • • • . 41 M. H. Manghnani, S. O. Schianger, and P. D. Milholland Application of Geophysical Methods 'and Equipment to Explore the Sea Bottom . •• •••. • 53 H. F. Weichart The Acoustic Response of Some Gas-Charged Sediments in the Northern Adriatic Sea • • • • . • • • • 73 A.
This publication documents the derivation of geoacoustic models for the Straits of Sicily and Sardinia-Tunisia. The geologic description of the region is based upon published geological/geophysical papers and archive data. The zone of primary concern is the first few hundred meters below the sea floor, which, in the present case, consists of unlithified Quaternary-Pliocene sediments. Lying below this upper layer is acoustic basement, which consists of Miocene chalks and limestones or evaporities. The modeling procedures developed by E.L. Hamilton were then used to estimate the physical properties of these sediment types. Finally, bottom loss as a function of grazing angle at a variety of frequencies was computed for the sea floor models. (Author).
