Joint migration velocity analysis of PP- and PS-waves for VTI media

Abstract

Combining PP-waves with mode-converted PS reflections in migration velocity analysis can help build more accurate VTI velocity models. To avoid problems caused by the moveout asymmetry of PS-waves and take advantage of efficient MVA algorithms designed for pure modes, I suggest to generate pure SS-reflections from PP and PS data using the PP+PS=SS method. Then the residual moveout in both PP and SS common-image gathers is minimized during iterative velocity updates. The objective function also includes the differences between the migrated depths of the same reflectors on the PP and SS sections and a regularization term. Synthetic examples confirm that 2D MVA of PP- and PS-waves may be able to resolve all four relevant parameters of VTI media if reflectors with at least two distinct dips are available. The algorithm is also applied to a 2D line from 3D OBS data acquired at Volve field in the North Sea.