旋转交错网格在横波分裂和再分裂模拟与分析中的应用

横波分裂可以用来探测地下介质的方位各向异性特征,如地幔流动方向、地壳内断层和应力的方向,以及近地表裂缝发育方位等,在地球深部结构探测和油气田勘探中具有重要作用。由于地下一般存在多层方位各向异性介质,记录的横波可能发生过多次分裂,因此,采用正演方法对横波分裂和再分裂进行数值模拟与分析,对于横波分裂反演和地下横向结构探测具有重要意义。旋转交错网格由于将速度和应力的不同分量置于同一网格点,可以避免各向异性参数的插值,正演更为精确。因此,采用旋转交错网格对方位倾斜横向各向同性介质的一阶速度-应力方程差分离散,并构造完全匹配层边界,实现了多层方位各向异性介质多分量逆VSP资料的正演;然后以此为基础,分析了横波发生分裂和再分裂时分裂参数随方位变化的规律;最后采用层剥离策略对多层方位各向异性进行反演和补偿,并探讨了层剥离方法的应用条件和技巧。

The Application of rotated staggered-grid finite-difference in the simulation of shear wave splitting and multiple splitting

Shear wave splitting can be used to detect azimuth anisotropy of Earth media, such as mantle flowing orientation, direction of maximum principle stressSand fracture azimuth in crust, so it plays an important role in both deep structure andSoil-gasSresourceSexploration. In general case, more than one layer can exhibit azimuth anisotropy, leading to one more splitting of single split shear wave. Therefore, the simulation of shear wave splitting and multiple splitting is a meaningful job for shear wave splitting inversion and lateral structure detection. Due to the good performance of rotated staggered-grid in wave field calculation of anisotropic media, it is used to calculate the reverse VSP multi-component records of a multiple azimuth anisotropy model in this paper. Then, the azimuth variation features of splitting parameters are analyzed under the conditions of singleSsplitting and multiple splitting. Finally, layer stripping technique is used to calculate and compensate multiple azimuth anisotropy, while its applying conditions and tips are discussed.