Abstract

The study of amplitude variations of reflected and transmitted seismic waves due to anisotropy has received considerable attention in recent years, but most investigations have concentrated on the effect of transverse isotropy with the symmetry axis either vertical or horizontal. The published results on the whole tend to exclude mode conversions. Amplitudes of all reflected and transmitted wave modes are addressed for P-waves incident on boundaries between isotropic and transversely isotropic media, the symmetry axis of which is oriented at 45 degrees to the interface. The results cover the full range of incidence angles and all 'acquisition azimuths' in the plane of the interface.When the anisotropy axis is not normal to the inter-face, the scattering coefficients are shown to be highly dependent on the azimuth. The pattern of azimuthal variation is especially complicated in the case of mode conversions, and scattering coefficient profiles that are 180 degrees apart are not the same. This has the implication that source-receiver interchangeability does not hold and could have serious consequences to amplitude studies in split-spread surveys.Both the P --> SV and P --> SH reflections show strong azimuthal variations, dependent on both the dip and the strike of the anisotropy axis. It may be possible to recover information about the orientation of the symmetry axis from observed scattering coefficients. It is also shown that the scattered amplitude patterns are dominantly controlled by the value of the elastic modulus c 13 .

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