First break traveltime tomographic imaging based on the eikonal equation in VTI medium
(2.Laboratory of Marine Mineral Resources Evaluation and Detection Techniques, National Laboratory for Marine Science and Technology, Qingdao, Shandong, China 266061)
【Abstract】The first break traveltime tomography is an effective method for the inversion of anisotropic parameter. Its difficulties are the calculation of first break traveltime and joint inversion of anisotropic parameters in VTI medium. In this paper, we use, NMO velocity, and non-elliptic coefficient to characterize the anisotropy. The ray tracing based on Runge-Kutta algorithm is used to calculate Fréchet kernel. According to the group slowness approximate expressions, the Fréchet kernels of these three parameters are derived. In order to overcome the magnitude between the three parameters, a double-round strategy is employed. The least squares orthogonal decomposition (LSQR) algorithm is used to carry out the joint inversion of the two methods. The numerical simulations show that the proposed method has better inversion accuracy than the Thomsen Kutta algorithm is not only applicable to isotropic medium but also to VTI medium.
【Keywords】 VTI medium; eikonal equation; first break traveltime tomography; Fréchet kernel; Thomsen parameter;
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