Abstract
Hereunder is presented a brief report of investigation made of the elastic anisotropy in rocks by the measurements of compressional wave velocity in the ultrasonic wave experiments. The velocities of compressional waves were measured at ordinary atomospheric pressure to 5 kilobars for Sanbagawa metamorphic rocks collected from various places in Shikoku, which were believed to be important constituents of the earth's crust. Three cylindrical specimens of 15mm in diameter and 45 to 50mm in length were cored from a block of rock samples by means of a diamond-impregnated boring machine. The orientations of the three specimens were mutually at right angles so as to coincide respectively with the three tectonic axes: a, b and c.The principal factors contributing to the wave-velocities in these rock samples of crystalline schists were investigated. The velocity variations due to pressure were empirically obtained asV(p)=Vf-AP-nin which A, n were constant paramaters indicating the speed of decrease in the porosity effect on wave velocity and also indicating elastic anisotropy. Vf was the velocity at pore-free condition at high pressures.The wave velocity along the b-axis was the largest and that along c-axis was the smallest. The largest difference in these wave velocities amounted to about 40% of the velocity along a-axis at the ordinary pressure and to about 10% at high pressures. The elastic anisotropy was great at lower pressure, decreasing with the increase of pressure. The relationship between wave velocity and density has been found to be V=α+βρ and β=2.20∼3.75 for crystalline schists.
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