Attenuation of Sound in Marine Sediments
Attenuation of sound in water-saturated sediments may be caused by frictional losses in the grain-to-grain contacts or to viscous loss due to the movement of the fluid relative to the solid frame. Both losses can be included in the Biot theory for sound propagation in porous media. This theory gives an attenuation coefficient for the frictional loss that is proportional to the frequency, f, and, a viscous attenuation increasing as f2 at low frequencies and as f½ in the high-frequency region.
The Biot theory depends on a number of parameters which are difficult to estimate, in particular for high-porosity silt and clay. In these cases one may instead use a model for the sound velocity and attenuation based on multiple scattering theory. This model gives the same frequency behaviour as the Biot model, but fails when the concentration of suspended particles exceeds a few percent. The reason for this is discussed, a modification to the suspension model is proposed, and the result compared with the Biot model. It is shown that, depending on the grain-size distribution viscous attenuation may also increase linearly with frequency over a wide frequency band.
KeywordsPorous Medium Bulk Modulus Marine Sediment Sound Velocity Sound Propagation
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