Waveform inversion based on wavefield decomposition

Abstract : Full Waveform Inversion (FWI) is a seismic imaging procedure to image the subsurface of the Earth. FWI is resolved as an optimization problem . Depending on the frequency content of the data, the objective function of FWI may be highly nonlinear. If a data set mainly contains reflections, this problem particularly prevents the gradient-based methods from recovering the long wavelengths of the velocity model.In this thesis, I propose a variant of FWI based on the wavefield separation, typically between up- and down- going waves, to mitigate the nonlinearity of the problem. The new method consists of decomposing the gradient of FWI into a short-wavelength part and a long-wavelength part after wavefield decomposition. The inversion is performed in an alternating fashion between these two parts. We apply this method to several case studies and show that the new method is more robust especially for constructing the long-wavelength model.
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Fang Wang. Waveform inversion based on wavefield decomposition. Geophysics [physics.geo-ph]. Ecole Nationale Supérieure des Mines de Paris, 2015. English. ⟨NNT : 2015ENMP0043⟩. ⟨tel-01299534⟩

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