弱横向各向同性介质中P波旅行时反演及速度分析

P-WAVE TRAVEL TIME INVERSION AND VELOCITY ANALYSIS IN WEAK TRANSVERSELY ISOTROPIC MEDIA

在各向异性介质中 ,由于反射波的相速度不等于群速度 ,其反射波时距曲线不再是双曲线。应用双曲线时差分析方法不能求取准确的叠加速度 ,当然就不能进行精确的速度分析 ,因而得不到精确的正常时差。文中阐述了横向各向同性介质中长排列的非双曲线的P波时差速度分析方法 ,即对P波的旅行时间进行泰勒展开 ,应用t2 ～x2 的四次方展开项进行时差速度分析。理论模型的反演结果表明 ,P波旅行时、叠加速度及水平速度都达到很高精度 ,且可求取Thomsen参数 η。

In anisotropy media, phase velocity of Pwave is generally different from group velocity, and the travel time-distance curve of reflected wave is not hyperbolic. So the analysis on hyperbolic moveout velocity can not be used to estimate stacking velocity accurately. Because it is impossible to make velocity analysis, the precise normal moveout can not be gotten. Hence, an analysis method of long spread nonhyperbolic normal moveout velocity for P wave in weak transverse media with vertical symmetry axis is illustrated. The quartic term of the Taylor series expansion for t 2\|x 2 curve is used to determine the normal moveout velocity. The inversion result of theoretical modeling shows that this method is available to get travel time, stacking velocity and horizontal velocity with high precision. Meanwhile Thomsen's parameter η\% can be obtained.