Full Waveform Inversion in an Anisotropic Earth: a Practical Workflow

An incorrect anisotropy in the Full Wave Inversion (FWI) velocity model leads to imperfect Common Image Gather (CIG) flatness. The main difficulty in the anisotropy estimation through FWI is the strong coupling with velocity. While FWI jointly updating velocity and anisotropy has been proposed, there is evidence that the long wavelength components of the velocity and anisotropic parameters cannot be reasonably decoupled inverting surface data only. The reason is that the long wavelength components of the velocity model inverted by FWI are mainly recovered from the kinematics of diving waves, while decoupling can only be done considering in addition the kinematics of reflected waves. To solve this challenge, we propose an innovative workflow involving joint reflection and diving wave tomography. To overcome the difficulty of first break picking, we propose a robust estimation of first arrival traveltime using the inverted FWI model of the first pass. With the application of this novelty on deep-water data from offshore Africa, we elaborate further with a sequence of first arrival modeling after tuned repositioning of sources and receivers at the sea floor.