Propagation of acoustic normal modes in a homogeneous ocean overlaying layered anisotropic porous beds

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Abstract
Attenuation of acoustic normal modes propagating in a shallow ocean overlaying naturally consolidated anisotropic sand beds is calculated using Biot’s theory for porous media. The propagator matrix method is utilized in the analysis to model layered transverse isotropic porous media. The effects of anisotropies in permeability and elastic moduli are studied numerically. It is found that the effect of the hydraulic anisotropy (permeability) of the sand bed on the acoustic attenuation is significant whereas the effect of the elastic anisotropy of the sand bed is not very important. The principle of relaxation is used to interpret the results. It is observed that the energy loss is maximum at a certain frequency which coincides with the relaxation frequency fr of the porous media given by fr=βν/3π ks. Here, β is the porosity, ν is the kinematic viscosity of the pore fluid, and ks is the coefficient of permeability.

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