Seismic Tomography from the Old to the New Millennium

During the past two decades, seismic tomography has been landing from the blue sky of academic or pioneering papers to the hard ground of industrial processing over a large scale. Actually, this happened for a few specific applications, such as tomostatics and velocity modeling for pre-stack depth migration. Other more recent or sophisticated developments, involving full waveform inversion or interferometry, are still maturing in terms of theoretical refinements or viable implementations. In this paper, I review the major practical or theoretical impact. I also propose a list of weak or missing items in the state-of-the art technology that needs to be addressed, to cope with current challenges in exploration, monitoring and production of unconventional tight gas.