Migration-based traveltime waveform inversion of 2-D simple structures: A synthetic example

Migration-based traveltime (MBTT) formulation provides algorithms for autom atically determining background velocities from full-waveform surface seism ic reflection data using local optimization methods. In particular, it addr esses the difficulty of the nonconvexity of the least-squares data misfit f unction. The method consists of parameterizing the reflectivity in the time domain through a migration step and providing a multiscale representation for the smooth background velocity. We present an implementation of the MBT T approach for a 2-D finite-difference (FD) full-wave acoustic model. Numer ical analysis on a 2-D synthetic example shows the ability of the method to find much more reliable estimates of both long and short wavelengths of th e velocity than the classical least-squares approach, even when starting fr om very poor initial guesses. This enlargement of the domain of attraction for the global minima of the least-squares misfit has a price: each evaluat ion of the new objective function requires, besides the usual FD full-wave forward modeling, an additional full-wave prestack migration. Hence, the FD implementation of the MBTT approach presented in this paper is expected to provide a useful tool for the inversion of data sets of moderate size.