Summary

We present a Kirchhoff prestack time migration technique for converted-waves (C-waves). This technique computes the C-wave diffraction travel time based on the exact travel time equations for v(z) VTI media. We demonstrate that it produces more accurate image than migration algorithms using travel time approximations. For anisotropic media, this technique requires four parameters: C-wave interval velocity vCi, interval vertical-travel-time ratio g0i, and Thomsen anisotropic parameters ei and di. For isotropic media, only vCi and g0i are required for the migration. We use pseudo-offset migration (POM) (Wang and Pham, 2001) to estimate C-wave velocities directly from the C-wave data. We show that C-wave velocity analysis is easier using POM gathers because the positions of dipping events are closer to their true conversion-point positions and conflicting events are reduced after POM