f Application of tomographic FWI (TFWI) to large-scale field datasets: challenges and insights.

In the past few years we have demonstrated with blind-test synthetic examples and 3D field-data examples that a time-lag extension of the velocity model can lead to robust convergence of FWI (we called our method Tomographic FWI or TFWI) even when the starting model is far from the correct one. Computational cost and convergence rate are still major obstacles to a routine TFWI application to large-scale projects. We will discuss recent advances in these areas.