Ray based approaches for velocity model building: past present and future

By mid 2000’s emergence of full waveform inversion (Virieux and Operto, 2009) has somehow occulted the progresses and perspectives of ray based velocity model building. Whatever by now velocity model building in industry remains still largely done using ray based approaches. Moreover, if breakthroughs have not been strongly put forwards for these techniques, they provide now solutions with unexpected resolution and accuracy. My aim here is to review these approaches and to investigate their future. The success and power of ray based approaches is strongly connected to a theoretical and numerical frame, which has been built around ray theory, and which offers a so powerful frame for the physical understanding of velocity model building. I first recall them before reviewing the various ray based velocity model building tools. Finally I discuss their connection with full waveform inversion approaches and discuss the perspectives.