Velocity model estimation using time-reversal focusing

Time reversal (TR) is a fundamental concept, consisting of time-reversing and re-propagating the registered wave-field in order to focus it at its true physical source. We propose a way to estimate the velocity model in a cross-hole survey by focusing the full registered wave-field to its source location after time reversal and back propagation. This approach allows for picking-free velocity analysis as well as the usage of global optimization techniques that are insensitive to the initial velocity model. Using a plane wave approximation of the timereversed data, we significantly reduce computation time and therefore propose a fully automatic and fast procedure for cross-hole velocity model building. We demonstrate the application of the method and its effectiveness on synthetic and field data examples.