Anisotropy of Poisson's Ratio in Rock Samples at Different Confining Pressures

Abstract Poisson's ratios calculated from VP=VS ratio can provide better constraints on the crustal composition than that from either the compresional or the shear velocity alone. To study the changes of Poisson's ratio and its anisotropy with confining pressure, we have measured P‐ and S‐wave velocities of 19 rock samples in three orthogonal directions at different confining pressures and calculated the Poisson's ratio and its anisotropy. The results show that for most samples there are some linear correlation between Poisson's ratio anisotropy and P‐wave velocity anisotropy. For some samples there are no such significant correlation. Some samples even show totally opposite changes in Poisson's ratio anisotropy and P‐wave velocity anisotropy. The Poisson's ratio of most rock samples is very markedly anisotropic, for some samples it is even greater than 30% when the effect of microcracks is eliminated. Therefore the anisotopy of Poisson's ratio must be considered when Poisson's ratio is used to inverse the crustal structure.