Staggered-grid forward modeling of qP wave in VTI media with improved acoustic approximation
LIANG Kai1,2, CHEN Haoran1, SUN Shangrao1, YIN Xingyao1,2
1. School of Geosciences, China University of Petroleum (East China), Qingdao, Shandong 266580, China; 2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, Shandong 266071, China
Abstract:The acoustic approximation proposed by Alkhalifah assumed the qSV wave velocity along the symmetry axis of the TI media to 0, and he established the corresponding qP wave equation and realized numerical simulations. However, there are two shortcomings. Firstly, there is a degenerate qSV wave solution in the equation, which is not a pure qP wave equation. Secondly, the equation is not applicable in media with ε< δ (ε and δ are the Thomsen parameter). Therefore, based on the work of Liang et al., the idea of improved acoustic approximation methods is introduced into the derivation of the dispersion relation and first-order wave equations for qP wave. The circular frequency in the accurate dispersion relation of the qSV wave is set to 0, and the elliptic decomposition is used to derive the decoupled dispersion relation of pure qP waves in VTI media. The spatial asymptotic approximation of the improved scalar operator is adopted to establish the qP wave first-order velocity and stress wave equations in VTI media with improved acoustic approximation. The staggered grid finite difference algorithm is used to achieve the forward simulation of pure qP wave in VTI media based on improved acoustic approximation. The analysis of dispersion relation and numerical examples show that the qP wave first-order equation with improved acoustic approximation does not include degenerate qSV waves and is a pure qP wave equation, which is in good agreement with the simulation results of the elastic wave equation and has high accuracy. The equation is stable in VTI media with both ε≥ δ and ε< δ and is applicable for complex VTI media.
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