GYROTROPY OF GRAINY AND THIN-LAYERED MEDIA

Abstract

The mechanism of origin of gyrotropy in a geologic medium has been simulated by models for grainy and thin-layered media having a dis symmetric microstructure. Calculation of displacements and stresses caused by a seismic wave is reduced to a static problem for each individual structural element of the medium (a grain or a thin layer), as they are negligeably small relative to the wavelength. The models are shown to be gyrotropic "rotating", i.e., the displacement vector of a shear wave in such a medium "turns" at an angle which is a sum of turns at each individual structural element of the model; the magnitude of these elementary rotation angles has been found to be equal to the parameter of medium dissymmetry. A numerical experiment has been carried out to reveal the main features of seismic-wave propagation in gyrotropic media. The calculation has shown that accessory components of displacements may occur not only in media with an azimuthal anisotropy but also in gyrotropic, for instance, transversely isotropic media with a vertical axis of symmetry.