不同围压下岩石中泊松比的各向异性

由弹性波纵横波速比计算得到的泊松比,在利用地震波反演地下结构和物质组成时,可以提供比单纯地利用纵波或者横波波速更强的约束. 为了研究不同岩石中泊松比及其各向异性随围压的变化,选取19块典型的岩石样品,在不同围压下沿相互正交的3个方向同时测量纵、横波速度,并通过计算得到了泊松比及其各向异性. 结果表明,在大部分样品中泊松比各向异性与纵波速度各向异性有一定的相关性,但在有的样品中泊松比各向异性与纵波速度各向异性没有明显的关系,甚至表现出完全相反的变化规律. 由于泊松比也表现出很强的各向异性,在排除微裂隙的影响后有的仍可以达到30髎以上,在利用实际地震波传播数据通过泊松比反演地下物质结构时必须考虑其各向异性的影响.

ANISOTROPY OF POISSON'S RATIO IN ROCK SAMPLES UNDER CONFINING PRESSURES

Poisson's ratios calculated from V_P/V_S can provide much tighter constraints on the crustal composition than either the compressional or the shear velocity alone. To study the changes of Poisson's ratio and its anisotropy with confining pressure, we measured P-and S-wave velocities in three orthogonal directions in 19 rock samples under different confining pressures. The results show that, in most samples there are some linear correlation between Poisson's ratio anisotropy and P-wave velocity anisotropy; while in some samples there are no significant correlation between them; some samples even show totally opposite changes in Poisson's ratio anisotropy and P-wave velocity anisotropy. Since in most rock samples Poisson's ratio is very markedly anisotropic, some even greater than 30% when the effect of microcracks is eliminated, the anisotopy of Poisson's ratio must be considered when using Poisson's ratio to inverse the crustal structure.