Combining PP-waves with mode-converted PS reflections in migration velocity analysis (MVA) can help build more accurate VTI (transversely isotropic with a vertical symmetry axis) 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 commonimage gathers is minimized during iterative velocity updates. The model is divided into square cells, and the VTI parameters V P 0 , V S0 , , and δ are defined at each grid point. 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 (ocean bottom seismic) data acquired at Volve field in the North Sea. After the anisotropic velocity model has been reconstructed, accurate depth images can be obtained by migrating the recorded PP and PS data.

Combining PP-waves with mode-converted PS reflections in migration velocity analysis (MVA) can help build more accurate VTI (transversely isotropic with a vertical symmetry axis) 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 commonimage gathers is minimized during iterative velocity updates. The model is divided into square cells, and the VTI parameters V P 0 , V S0 , , and δ are defined at each grid point. 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 (ocean bottom seismic) data acquired at Volve field in the North Sea. After the anisotropic velocity model has been reconstructed, accurate depth images can be obtained by migrating the recorded PP and PS data.

Mode-converted PS-waves can provide valuable information for anisotropic parameter estimation that cannot be obtained from compressional waves alone. In a previous paper, we developed an efficient tomographic methodology for 2D joint velocity analysis of PP and PS data from VTI (transversely isotropic with a vertical symmetry axis) media. The algorithm is designed to flatten image gathers of PP-waves as well as of pure SS reflections computed using the PP+ PS = SS method. An important additional constraint is provided by codepthing of the migrated PP and SS sections. The model is divided into square cells, and the parameters V P 0 , V S0 , , and δ are defined at each grid point. Here, this methodology is applied to multicomponent data recorded on a 2D line from an OBS (ocean bottom seismic) survey acquired at Volve field in the North Sea. Although the parameter-updating procedure did not include any borehole information, the VTI model obtained by joint tomography of the recorded PP-waves and constructed SS-waves produced generally well-focused PP and PS depth images. The depth consistency between the migrated PP and PS sections also corroborates the accuracy of the velocity-analysis algorithm.