Elastic properties of Kola overdeep borehole (SG-3) samples determined under atmospheric and in situ conditions

The ultrasonic method was applied to the deteemination of anisotropic elastic properties of core samples from a 40- to 12014-m depth interval of the Kola overdeep borehole. Unloaded samples under atmospheric conditions and samples at in situ pressures and temperatures in special apparatuses were measured. The elastic anisotropy parameters measured in samples under both laboratory conditions and P-T conditions corresponding to sampling depth allow one to divide the Kola hole section into two parts. Isotropic and weakly anisotropic rocks generally dominate in the upper part, down to a depth of 4.5 km. It is important that measurements under laboratory in situ conditions confirmed high anisotropy of rocks in a depth interval of 6.3-10.2 km, which is a large portion of the SG-3 section. The inferred anisotropy parameters are significantly greater than the level below which they may be neglected. In general. results of this work show that deep Proterozoic and Archean metamorphic crystalline rocks of the upper and middle crust can be highly anisotropic.