声学各向异性介质中的S波

声学VTI介质是人为定义横波在对称轴方向的速度V_S0的一种模型。传统理论认为当V_S0=0时可以消除横波能量。论证声学VTI介质的存在，并讨论其特殊的性质，可以看到在声学VTI介质中SV波的相速度和群速度并不是恒为零。用高阶交错网格有限差分方法对不同的声学VTI介质模型进行全波场模拟，同时计算V_s0取不同值时的群速度和相速度x、z分量。通过对比分析得出波现象：SV波在垂直方向传播时其极化方向是平行于P波传播方向的；由于邻近方向能量的聚集，在对称轴附近SV波的振幅会有较大的值；P波和SV波的群速度的值在某些方向上可以很接近甚至相等。

S WAVE IN ACOUSTIC ANISOTROPIC MEDIA

Acoustic VTI media is a kind of model which is artificially defined as a velocity V_S0 for shear wave on symmetry axis.Contrary to the conventional theory that whenV_S0 equals to zero,shear wave is eliminated,the existence of acoustic VTI media is demonstrated and its properties examined.Specifically,it is pointed out that SV wave generally has finite nonzero phase and group velocities in acoustic VTI media.This phenomenon can be observed in fullwave field simulation,which,however,was concluded as artificial numerical pseudomorph in the past.The most obvious characteristic of acoustic VTI media is extreme anisotropy,which under certain circumstances would present infinite anisotropy.Several fullwave field simulations have been established for different acoustic VTI media models,by adopting the finite deference method with highorder crossed grids,the x,zcomponents of group velocity and phase velocity are calculated respectively when V_S0 is given different values.The following wave performance can be achieved through comparison and analysis,the polarization direction of Vwave propagating vertically in acoustic VTI media parallels to that of Pwave propagating in the same direction,amplitude of SVwave is large due to concentration of energy in the vicinity of the symmetry axis,the group velocities of Pwave and SVwave can be very close or even equal to each other.