Nouveaux algorithmes efficaces de modélisation 2D et 3D : Temps des premières arrivées, angles à la source et amplitudes

Abstract : Traveltimes, amplitudes and take-off angles of seismic waves are used in many applications such as migration, tomography, detection sensitivity estimation and microseism location. In the microseismicty context it is necessary to compute in near real time accurately these attributes. Here we developed a set of fast and accurate algorithms in 3D for highly contrasted velocity models.We present a new accurate method for computing first arrival traveltimes, amplitudes and take-off angles; more precisely we solve the Eikonal, transport and take-off angle equations based on a finite difference approach for 3D velocity models. We propose a new hybrid method that benefits from the advantages of several existing Eikonal solvers. Common approaches that solve directly these equations assume that we are locally propagating a plane wave. This approximation is not well adapted in the neighborhood of the source since the wavefront curvature is important. Travel times errors are generated near the source position and then propagated through the whole velocity model. This prevents from properly calculating the amplitudes and the take-off angles since they rely on the travel time gradients that are not accurate. We overcome this difficulty by introducing spherical operators. Indeed we reformulate the traveltimes, amplitudes and take-off angles with the perturbation method.We validate our new methods on various highly contrasted velocity models in 2D and 3D and show our contribution compared to other existing approaches. Our results are similar to those computed using full waveform modeling while they are obtained in a much shorter CPU time. These results open thus new perspectives for several applications such as migration, detection sensitivity estimation and focal mechanism inversion.
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Nidhal Belayouni. Nouveaux algorithmes efficaces de modélisation 2D et 3D : Temps des premières arrivées, angles à la source et amplitudes. Sciences de la Terre. Ecole Nationale Supérieure des Mines de Paris, 2013. Français. ⟨NNT : 2013ENMP0012⟩. ⟨pastel-00871200⟩

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