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在各向异性介质中,短排列叠加速度一般不同于均方根垂直速度。即使有P波和S波两种波,由于各向异性的影响,不可能对短排列、共中心点(CMP)道集进行双曲时差分析求得垂直速度(或反射面深度)。因此,我们探讨适合具有垂直对称轴的横向各向同性介质参数、长排列(非双曲线)反射时差反演的可行性。一个可能的解是恢复P波和SV波t~2—x~2曲线的泰勒级数展开式的四次项,并用其确定各向异性。然而,由于中排列(即大约是反射面深度1.5倍的排列),P波和SV波时差联合反演的非单值性,这一方法不稳定。如仅存在P波数据,使用长排列(反射面深度的两倍)则不能克服非单值性。P波反演问题的全面分析说明,存在一大套不同垂直速度的模型可以满足其拟合精确的旅行时。通过有限角域道集上各向异性介质参数与垂直速度间的权衡,可解释这种表现很强的非单值性。长排列的P波和SV波时差相结合,可明显增加反演精度。长排列SV波时差对反射面深度的高灵敏度使反演的非唯一性减小。在某些情况下,SV波时差可单独用于求取垂直S波速度,进而求取深度。该反演成功与否取决于排列长度和SV波速度的各向异性程度以及P波垂直速度的约束。
In anisotropic media, the short-run stacking speed is generally different from the root-mean-square vertical speed. Even with two types of P-wave and S-wave, it is not possible to obtain vertical velocities (or depths of reflection surfaces) by hyperbolic time-lapse analysis of short-aligned, co-centered (CMP) gathers due to anisotropy. Therefore, we explore the feasibility of using transversely isotropic media parameters with a vertical axis of symmetry and long-time (non-hyperbolic) reflections with time-difference inversion. A possible solution is to recover the fourth order of the Taylor series expansion of the t ~ 2-x ~ 2 curves of P-wave and SV-wave, and use it to determine the anisotropy. However, this method is not stable due to the non-monomorphic inversion of the mid-range (ie, approximately 1.5 times the depth of the reflector surface) inversion of the P- and SV-wave time differences. If only P-wave data exists, the use of long permutations (twice the depth of the reflecting surface) can not overcome non-singularity. A comprehensive analysis of the P-wave inversion problem shows that there are a large set of models with different vertical velocities to fit their exact travel time. The trade-off between anisotropy medium parameters and vertical velocities over finite angular gathers accounts for this strong nontriviality. Long array of P wave and SV wave time difference combination can significantly increase the accuracy of inversion. The high sensitivity of the time-varying SV waves to the depth of the reflector reduces the non-uniqueness of the inversion. In some cases, the SV wave-time difference can be used alone to determine the vertical S-wave velocity and thus the depth. The success or failure of the inversion depends on the degree of anisotropy of the arrangement length and SV wave velocity and the constraint of the P-wave vertical velocity.