Seismic data have long been processed and imaged under the isotropic wave propagation assumption. Despite the abundant amount of shaly sediments in the Earth’s subsurface with well-known anisotropic material composition, as well as, the natural sedimentation process that has a general vertical preference, we typically resorted in the 1990’s to isotropic imaging algorithms. Only recently, starting around the early 2000s, that imposing anisotropic medium assumptions to wave propagation and imaging saw wide spread appeal and now it is part of the mainstream seismic data imaging process in many places. The reason for this development is three fold: 1) the higher resolution, longer offsets, multi azimuth nature of our acquisition nowadays, 2) the advancement in simplifying the anisotropy description and representation, including resorting to the acoustic assumption, and finally, 3) the tremendous return for investment seen in seismic images produced by including anisotropy in imaging.

 

Advancement in simplifying the anisotropic medium representation and imaging is still underway including simplifications in representing the depth axis with pseudo depth that allows us to eliminate the dependency on the, usually elusive from surface seismic data, vertical velocity. We also saw recently simplifications in describing the transversely isotropic medium (TTI) tilt using a structural conformable approach and more so by replacing TTI with a dip-oriented model (DTI). In this case many of the equations that we use for angle gather decomposition as well as imaging are simple, simpler than even those associated with the vertical symmetry TI (VTI) case. All this advancement is done under, what is now considered, the conventional acoustic assumption, and this assumption has recently been applied to the titled orthorhombic case. We also saw recently witnessed the development of methods to decompose the image point after reverse time migration to reflection angles and azimuths for such media. This will provide us with anisotropy velocity quality control tools that are also useful for updating the velocity model as well as assessing the illumination properties of our acquisition in TTI media.