NORMAL MOVEOUT IN ANISOTROPIC MEDIA

A general expression for NMO velocity has been derived for a CMP gather above a dipping reflector in an elliptically anisotropic medium in which the velocity function has arbitrary orientation. VNMO is constant for a given plane reflector dip angle and velocity orientation, and is independent of offset. The NMO velocity is equal to the horizontal component of the velocity function only if the reflector is horizontal. In anisotropic media for which the velocity function is nonelliptical, the method of images does not apply and the NMO velocity is a function of offset. The existence of a possible spread of reflection points must be remembered when an approximate stacking velocity is used for stacking such data. -from Authors