First break traveltime tomographic imaging based on the eikonal equation in VTI medium
Zhang Kai1,2, Chen Junyi1,2, Zhu Baihang1, Li Zhenchun1,2, Ding Pengcheng1
1. School of Geosciences, China University of Petroleum(East China), Qingdao, Shandong 266580, China; 2. Laboratory of Marine Mineral Resources Evaluation and Detection Techniques, National Laboratory for Marine Science and Technology, Qingdao, Shandong 266061, China
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 three parameters including the vertical velocity,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 group slowness approximate expressions,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.Numerical simulations show that the proposed method has a better inversion accuracy than the Thomsen method,and the ray tracing based on the Runge-Kutta algorithm is not only applicable to isotropic medium but also to VTI medium.
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