Shear‐wave velocity anisotropy in sedimentary rocks: A laboratory study

Abstract

A systematic laboratory study of shear‐wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress. The presence of shear‐wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver. The magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample. Shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress, which suggests the presence of preferentially aligned minerals. Sandstones also exhibit significant velocity anisotropy, but the anisotropy is strongly dependent upon the stress. Hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it. This implies the presence of preferentially oriented cracks. Limestones exhibit weak velocity anisotropy. These laboratory observations may be helpful in in situ identification of lithology.