2D synthetic data example

Figure shows an anisotropic model with a thrust sheet embedded in the isotropic background Fei et al. (1998). Figure (a) shows the tilting angle of the thrust, Figure (b)-(d) show the velocity, the anisotropy parameters $\varepsilon$ and $\delta$ of the model, respectively. This model represents the thrust shale layer usually seen in the Canadian Foothills. In the thrust sheet, the anisotropy parameter $\varepsilon$ is 0.224, the anisotropy parameter $\delta$ is 0.10, and the velocity ( in the direction paralleling to the symmetry axis) is 2925m/s. The background velocity is 2740m/s. The tilting angles of the anisotropic layer are $0^\circ$, $30^\circ$, $45^\circ$ and $60^\circ$.There are 86 shots recorded with a split-spread geometry.

Figure compares images of the synthetic dataset. Figure (a) is the image migrated by using an isotropic migration, Figure (b) is the image obtained by an anisotropic migration regarding the model as VTI media Shan (2006b), and Figure (c) is the image obtained by an anisotropic migration for TTI media. In Figure (a) and (b), the low boundary of the thrust sheet are not at the right position and the flat reflector does not focus at the right position in the area below the thrust sheet (at "A"). These features are imaged well in Figure (c) by the anisotropic migration for TTI media.

 

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Figure 4 Image comparisons: (a) the image obtained by the isotropic migration; (b) the image obtained by anisotropic migration for VTI media; (c) the image obtained by anisotropic migration for TTI media.

At "B", the low boundary of the $60^\circ$ thrust sheet is better imaged in the isotropic migration (Figure (a)), compared to the migration for VTI media (Figure (b)). For the high-angle energy in a TTI medium with a large tilting angle, the velocity of the waves is close to the velocity in the symmetry-axis direction. When we regard the medium as a VTI medium, for the high-angle energy we use the velocity close to the velocity in the direction normal to the symmetry axis. In contrast, we use the velocity paralleling the symmetry axis in the isotropic migration. That is why the low boundary of the $60^\circ$ thrust sheet at "B" is better imaged by the isotropic migration compared to the anisotropic migration for VTI media.