Usefulness of the Interface Fresnel zone for simulating the seismic reflected amplitudes
Résumé
The aim of the paper is to emphasize the importance of accounting for the Fresnel volume (FV) and for the Interface Fresnel zone (IFZ) for simulating the amplitudes of the spherical waves reflected from an interface between elastic media and recorded at the receiver. For this purpose, by considering the problem of interest as a problem of diffraction by the IFZ, we have developed a method wich combines the Angular Spectrum Approach (ASA) with the IFZ concept to get the 3D analytical solution. The comparison between the amplitude-versusangle curve predicted by our approximation with that predicted by the classical plane-wave theory, and also with the exact solution, clearly enlightens three points. First, for specific regions of incidence angles, for which the geometrical-spreading compensation is not sufficient anymore to reduce the point-source amplitudes to the plane-wave amplitudes, the additional application of the FV and of IFZ concept is necessary. Second, as our approximation is concerned only with the reflected wave, its predictions fit well the exact solution, provided there is no interference between the reflected wave and the head wave. Third, they exhibit oscillations in the postcritical region which result from the interference of the IFZ with the sharp edge of the reflection coefficient.
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