### ASA 124th Meeting New Orleans 1992 October

## 4pPA1. Spherical wave propagation in layered poro-elastic and fluid
systems.

**Keith Attenborough
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*Eng. Mech. Discipline, Open Univ., Milton Keynes MK7 6AA, England
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**Shahram Taherzadeh
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*The Open University
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A numerical procedure for computing sound propagation from a point source
in an environment consisting of a stratified fluid half-space above a layered
poro-elastic ground is described. The wave amplitudes are computed from
depth-separated wave equation by forming a system of linear equations arising
from the boundary conditions at each and every interface between layers and
solving the resulting global matrix. The inverse Hankel transform is then
performed by fast Fourier method (FFP) to obtain the pressure and particle
velocity at any elevation as a function of range. Wave propagation within the
porous elastic layers is calculated according to the modified Biot--Stoll
theory which predicts two compressional and one shear wave types in the medium.
Six boundary conditions are therefore required at each ground intefaces and
four at the fluid--ground interface, while only two are needed at the
fluid--fluid interfaces. Using this code the role of the ground elasticity on
above-ground propagation and in acoustically induced seismic excitation are
explored. It is predicted that on certain ground types, characterized by a thin
layer with small compressional and shear velocities, and at frequencies that
coincide with a peak in the seimic-to-acoustic coupling ratio spectrum there is
an extra sound attenuation.