In Situ Determinations of the Velocities of Compressional and Shear Waves in Marine Sediments from a Research Submersible


Book Description

In situ measurements were made of the velocity and attenuation of compressional waves and of velocities of Stoneley waves (from which shear-wave velocities were computed) at six stations in the sea floor off San Diego, California. Water depths ranged from 20 to 1130 meters, and sediment types ranged from medium sand to clayey silt. Sediment densities, porosities, and grain sizes were measured in samples taken at each station. The unique data obtained allowed tentative evaluations of models and equations, and computation of constants, for elastic and viscoelastic saturated, porous media. (Author).




Shear Waves in Marine Sediments


Book Description

Shear waves and closely related interface waves (Rayleigh, Stoneley and Scholte) play an important role in many areas of engineering, geophysics and underwater acoustics. In some cases interest is focused on large-amplitude waves of low frequency such as those associ ated with earthquakes and nuclear explosions; in other cases low amplitude waves, which have often travelled great distances through the sediment, are of interest. Both low and high frequency shear and interface waves are often used for seafloor probing and sediment characterization. As a result of the wide spectrum of different interests, different disciplines have developed lines of research and a literature particularly suited to their own problems. For example water-column acousticians view the seafloor sediment as the lower boundary of their domain and are interested in shear and interface waves in the near bottom sediments mainly from the standpoint of how they influence absorption and reflection at this boundary. On the other hand, geophysicists seeking deep oil deposits are interested in the maximum penetration into the sediments and the tell-tale characteristics of the seismic waves that have encountered potential oil or gas bearing strata. In another area, geotechnical engineers use shear and interface waves to study soil properties necessary for the design and the siting of seafloor structures.













Acoustic Relaxation in Unconsolidated Marine Sediments


Book Description

Acoustic relaxation theory for visco-elastic media provides for sound propagation in unconsolidated marine sediments. For the frequency range of 14 to 200 kHz, dispersion for compressional-wave and shear-wave velocity is negligible for all practical purposes, but sound absorption shows significant changes. (Author).







Determination of Compressibility of Marine Sediments from Compressional-Wave Velocity Measurements


Book Description

Knowledge of the compressibility of marine sediments is required for the design of adequate foundations for offshore installations. The determination of compressibilities of sediments by standard laboratory tests necessitates expensive sampling. Empirical relationships between void ratios, coefficients of compressibility and seismic velocities have been established by comparing laboratory consolidation tests with simultaneous compressional-wave velocity determinations for clay muds representative of four environments of the Gulf of Mexico. (Author Modified Abstract).




Acoustic and Related Properties of the Sea Floor


Book Description

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.