Full waveform inversion (FWI) is a powerful tool to resolve high-resolution subsurface physical properties. As a nonlinear and computationally intensive problem, FWI is usually solved by local optimization method, which requires accurate knowledge of background velocity. Ray-based traveltime tomography, as a conventional method to retrieve long wavelength structure, is widely applied to get starting model for FWI. However, the resolution is restricted by the intrinsic limitation of ray approximation and tomography can hardly resolve low velocity zone. Wave equation tomography, on the other hand, can explore the finite-band feature of seismic wavefield and hence gain better resolution than ray-based tomography. Therefor wave equation tomography can provide more sufficient starting model for FWI. Furthermore, wave equation tomography can be solved by adjoint method, which is similar to FWI. So we propose a hybrid misfit function to combine wave-equation tomography and FWI as an integrated strategy that is able to estimate high-resolution structure from poor starting model.


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