New approximate expressionS of Seismic group velocities for weakly anisotropic media
一种弱各向异性介质地震波群速度的近似表示新方法

Group velocities of seismic waves in anisotropic media are usually expressed as functions of phase angle instead of ray angle for it is difficult for general anisotropic media to express them in terms of the latter.However,expressions of the group velocities in terms of ray angle are needed in calculating travel times for anisotropic media and in analysis of seismic anisotropy.Fortunately,most media in the Earth's interior are weakly anisotropic,which makes it possible to approximately write the group velocities as functions of ray angle.In this paper,we have put forward a new method to approximately express the group velocities in terms of ray angle for weakly anisotropic media.The new method is based on the approximate expression of phase angle in terms of ray angle.Numerical examples show that the new formula can approach well the exact group velocities of the three kinds of waves during a wide range of ray angle,and,especially,it has much higher accuracy than other expressions for quasi-SV waves.