RAY-BASED 2D ANISOTROPIC PRE-STACK DEPTH MIGRATION ON SYNTHETIC AND REAL DATA

Pre-stack depth migration (PSDM), while costly, is a powerful tool for imaging and velocity analysis. Seismic velocity anisotropy is now tho ught to be widespread in sedimentary rocks, particularly shales. We ha ve written a 2D pre-stack depth migration code for use in transversely isotropic media with a Vertical symmetry axis (TIV). We use it to inv estigate the effects of anisotropy on isotropic pre-stack migration by means of a simple synthetic example. Results suggest that it is diffi cult to find plausible isotropic models which give good images of refl ectors at all dips. We further apply our PSDM code to a 2D line of rea l data from offshore West Africa, where there is a thick shale sequenc e, using isotropic and anisotropic velocity models. A dipping fault pl ane is imaged more clearly with the anisotropic model, but some of the near horizontal reflectors are less well imaged suggesting that this model could be improved and confirming the sensitivity of pre-stack de pth migration to all aspects of the velocity model.