부산대학교 도서관

The presence of fractures and textures cause metamorphic rock masses to be seismically anisotropic. Neglect of this anisotropy in the processing of field seismic data causes problems in the final reflection images both in terms of their quality and in the true positioning of subsurface features. To quantify the degree of seismic anisotropy in the subsurface, one method is to estimate the anisotropic parameters from the elastic stiffnesses of a rock sample. Using the ultrasonic pulse transmission method, measurements of the compressional and shear wave phase velocities as a function of confining pressure are used to calculate the elastic stiffnesses of a metamorphic granite core sample from the Precambrian basement in northeastern Alberta. Velocities are measured parallel, normal and oblique to an identified foliation plane of the sample assumed to be a transversely isotropic medium. The compressional wave velocities are measured to be in the range of 5,352-6,019 m/s along the foliation plane and 4,752-5,396 m/s normal to the foliation plane over the range of confining pressures from 0 to 60 MPa. Besides providing valuable in situ velocity information for the velocity models, the results also confirm the anisotropic behavior of the metamorphic rock with the estimated compressional and shear wave anisotropy valued at 12 and 8 %, respectively. Such degree of seismic anisotropy should be taken into consideration at the seismic scale when working with three-dimensional geophysical models of the Precambrian basement to minimize any out-of-plane anomalies in the final seismic sections. [ABSTRACT FROM AUTHOR]