Anisotropic Velocity Analysis in VTI Media by Duplex Wave Migration

With synthetic examples, a method for evaluating vertical velocity and Thomsen’s anisotropic parameters and in isotropic and vertical transverse isotropic (VTI) media is demonstrated. The method uses duplex wave migration (DWM) as the engine that determines these parameters. One of the characteristics of DWM based velocity analysis is that it’s resolving power increases (rather than decreases) with depth. With DWM, seismic images of vertical boundaries in a narrow range of transformation apertures are formed. It allows group velocities in VTI media to be determined with a rather high accuracy. With these velocities, Thomsen parameters and vertical velocities are evaluated. The area in which the above parameters are determined is much smaller than for conventional PSDM based velocity analysis using sub-horizontal boundaries. Therefore, this method enables improved resolution of local lateral changes in anisotropic velocity parameters.