Assessments of Elastic Anisotropy of Banded Amphibolite as a Function of Cleavage Orientation Using S- and P-Wave Velocity

Abstract

As most rocks are of an anisotropic nature, the measurement elastic modulus of anistropic rocks is of general interest. Nevertheless, uniaxial compression test is common method to measure the dynamic elastic constants of anisotropic rocks; the use of ultrasonic pulse test is attractive, because the test is non-destructive and easy to apply. This study aimed to demonstrate the influence of orientation of foliation planes of banded amphibolite rocks on the compressional (Vp), shear wave (Vs) velocities propagating and elastic modules using ultrasonic pulse test. The result showed that the planes of foliation have a major effect on the wave velocity, where the Vp and Vs were taken parallel to the foliation plane show highest values than those obtained in the other directions (β = 30˚, 60˚ and 90˚). The preliminary conclusions are developed concerning that the elastic modulus is vary continuously as a function of cleavage orientation with respect to the direction of wave propagations, where Poisson’s ratio having the smallest relative change. The highest values of Young’s modulus and shear modulus are observed for foliation dip angles of 0˚ and the lowest values are for foliation dip angles of 90˚. This indicates that the observed intrinsic anisotropy and the close relations of the directional dependent seismic anisotropy to the foliation planes are mainly a result of crystallographic preferred orientation of major minerals (e.g. hornblende and elongated quarts grains).