关键词: 声学各向异性, 群速度, 相速度, 有限差分, VTI介质

Abstract: 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.

Key words: acoustic anisotropic, group velocity, phase velocity, finite deference method, VTI media