Anizotropia prędkości fal sejsmicznych i jej związek z orientacją systemów spękań masywów skalnych

Abstract

Fracturing is one of the fundamental characteristics of the Earth crust. It has a governing influence on many physical properties of the rock massifs. Due to the importance of fracturing, of great significance becomes the feasibility of determining crack parameters in massifs which are not directly accessible for geological observations. Joint exert a particularly marked influence on the elastic properties of the rocks and hence on the seismic wave velocities. The existence of this relation makes it possible to use of seismic methods for determining the crack density and the orientation of crack systems. In these studies the objective was to determine the relationship between crack anisotropy and seismic wave velocity anisotropy using of the most up to date interpretation method based on tensor calculus. The concept of crack tensor developed by Oda (1984, 1986) was modified so as to give it a specific physical sense. At the same time the constituent equation was also modified and in this way the values of elastic constants calculated from the crack distribution corresponded to values found by seismic methods. A detailed analysis was made of the two-dimensional crack tensors and velocity tensors in the transversely isotropic medium. Their characteristic features were shown on the model distributions of velocities and cracks. From the results of experimental tests carried out in carbonate massifs of varied ages lying in the eastern and north — eastern part of the Upper Silesian Coal Basin it was possible to verify the theoretical model developed, by establishing the relations between the components of crack tensors and velocity tensors in the massifs considered. A procedure was developed for determining joint distributions from seismic measurements. Obtained results can be utilized in tests of jointed rocks inaccessible for direct observations.