Wave reflection at an anelastic transversely isotropic ocean bottom

Abstract

We study the reflection of waves at the ocean bottom, which is modeled as a plane interface separating a viscoacoustic medium (water) and a viscoelastic transversely isotropic solid whose axis of rotational symmetry is perpendicular to the bottom. We compute the plane-wave reflection coefficient (including the phenomenon known as the Rayleigh window) both numerically — by amplitude variation with offset (AVO) analysis of synthetic seismograms generated using a domain decomposition method and analytically. A first simulation considers the water-steel interface, for which experimental data is available. Then, we consider soft sediments and stiff crustal rocks for various values of the anellipticity parameter [Formula: see text]. The domain-decomposition technique relies on one grid for the fluid and another grid for the solid and uses Fourier and Chebyshev differential operators. The ane-lastic and anisotropic stress-strain relation is described by the Zener model. Special attention is given to modeling the boundary conditions at the ocean bottom. For this purpose, we further develop the technique for wave propagation at fluid/anelastic-anisotropic-solid interfaces. AVO slowness-frequency-domain analysis is used to compute the reflection coefficient and phase angle from the synthetic seismograms. This allows us to verify the domain-decomposition algorithm, which is shown to model with high accuracy the Rayleigh window for varying [Formula: see text]. The comparison also verifies the calculation of the analytical plane-wave reflection coefficient because a wrong choice of the sign of the vertical slowness of the reflected wave may cause nonphysical discontinuities in the coefficient. Moreover, the pseudospectral modeling code allows a general material variability and a complete and accurate characterization of the seismic response of an anisotropic ocean bottom.