Seismic wave simulation by velocity–stress wave equations in two-phase anisotropic media

Abstract

In two-phase anisotropic media, fast P-waves, slow P-waves and SV-waves are coupled with each other. Fast P-wavefronts show an elliptical anisotropic feature. Although the wavelet phase of the fast P-wavefront in a solid and that in a fluid are the same, the wavelet phases of the slow P-waves are opposite. In cases where there is an obvious slow P-wave in the wavefield, the slow P-wave in fluid is stronger than that in the solid. The attenuation mechanism introduced in Biot's theory is of secondary importance for the fast P-wave and the SV-wave, but dissipation coefficients have a significant effect on the slow P-wave. If there is a large dissipation in the media, the slow P-wave will be attenuated very quickly. When the dissipation coefficients have strong anisotropy, the slow P-wave is attenuated not just along the direction that has a big dissipation coefficient, but for the entire slow P-wavefield. Hence the slow P-wave is hardly observable in practice on surface seismic records. It is clearly a limitation of conventional seismic analysis which we should be aware of in reservoir geophysics.