Kirchhoff prestack depth scalar migration of complete wave field using the prevailing-frequency approximation of the coupling ray theory

Vaclav Bucha

Summary

The coupling ray theory provides more accurate polarizations and travel times of S waves in models with weak anisotropy than the anisotropic ray theory. We test the application of the prevailing-frequency approximation of the coupling ray theory to 3-D ray-based Kirchhoff prestack depth scalar migration and compute migrated sections in two simple inhomogeneous weakly anisotropic velocity models composed of two layers separated by a curved interface. The recorded complete seismic wave field is calculated using the Fourier pseudospectral method. We use a scalar imaging for the complete wave field in a single-layer velocity model with the same anisotropy as in the upper layer of the velocity model used to calculate the recorded wave field. We migrate reflected PP, converted PS1 and PS2 elementary waves without the separation of the recorded complete wave field. For migration of the S wave part we use the prevailing-frequency approximation of the coupling ray theory and for comparison we apply the anisotropic-ray-theory approximation. Calculations using the prevailing-frequency approximation of the coupling ray theory are without problems for both models. On the other hand, for the anisotropic-ray-theory approximation in the model with weaker anisotropy we have to use limitation of Green function maxima otherwise the migrated sections are wrong. In spite of complex recorded wave fields, without decomposition, the migrated interfaces for the vertical component of the PP reflected wave, radial and transversal components of PS1 and PS2 converted waves are in all stacked migrated sections relatively good with exception of spurious interface images close to the correct ones.

Keywords

Fourier pseudospectral method, 3-D Kirchhoff prestack depth scalar migration, anisotropic velocity model, weak anisotropy, complete wave field, coupling ray theory

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Seismic Waves in Complex 3-D Structures, 31 (2022), 7-29 (ISSN 2336-3827, online at http://sw3d.cz).