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Adjoint slope tomography : a velocity macro-model building tool for seismic imaging

Abstract : Velocity macro-model building is a crucial step in seismic imaging workflows as it provides the necessary background model for migration or full waveform inversion. Slope tomography, as a reliable alternative for conventional tomography, provides a tool to achieve this purpose where one picks the local coherent events rather than continuous events. These approaches are based on the slopes and traveltimes of the local coherent events which are tied to a reflecting/diffracting point (scatterer) in the subsurface. In this thesis, I introduce an anisotropic slope tomographic approach which aim at macro-model building for subsurface properties in 2D tilted transversely isotropic (TTI) media. In this method, I reformulate the stereotomography, as an slope tomographic tool, such that I replace the ray-based forward engine with a TTI eikonal solver and take advantage of the adjoint state method to calculate the gradients. In result, I can efficiently calculate the traveltimes for complex media and long offset acquisition on a regular grid of the subsurface and formulate a matrix-free framework for the inversion. Different synthetic examples including the isotropic Marmousi and 2D TTI BP-salt model are considered to assess the potential of the method in subsurface parameter estimations. Also, through a simple example, the footprint of parameter cross-talk is investigated for the Thomsen parametrization. As a real data application, the proposed method is applied on a 2D marine BroadSeis data set (provided by CGG) to retrieve the vertical velocity of the subsurface.
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Borhan Tavakolifaradonbeh. Adjoint slope tomography : a velocity macro-model building tool for seismic imaging. Earth Sciences. COMUE Université Côte d'Azur (2015 - 2019), 2017. English. ⟨NNT : 2017AZUR4089⟩. ⟨tel-01782404v2⟩

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