Effect of foliation orientation on the P- and S-wave velocity anisotropies and dynamic elastic constants of the quartz-m
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ORIGINAL PAPER
Effect of foliation orientation on the P- and S-wave velocity anisotropies and dynamic elastic constants of the quartz-micaschists metamorphic rocks, Angouran mine, Iran Ramin Nikrouz 1 & Hassan Moomivand 2 & Rashid Azad 1
Received: 1 February 2016 / Accepted: 29 September 2016 # Saudi Society for Geosciences 2016
Abstract Laboratory measurements are required to study geophysical properties of the subsurface because of lacking direct observation of Earth’s crust. In this research, compressional (P) and shear (S) wave velocity measurements have been conducted on cylindrical specimens of Quartzmicaschist cored using rock blocks taken from the zinc and lead Angouran mine, Zanjan, northwest of Iran. Cylindrical rock specimens were prepared from the blocks by coring in 0°, 30°, 45°, 60°, and 90° into the foliation direction. P- and Swave velocities were measured along the cylindrical specimens with different foliation orientations. Percent variations of the P- and S-wave velocities (Thomsen’s anisotropic parameters ε and γ) and constant dynamic modulus of test results have been determined. Percent variations of the P-wave velocity (ε) increase with an increase of the foliation angle with respect to the propagating waves direction by a parabolic function as it shows P-wave velocity differences up to a maximum value of 50 %. Thomsen’s anisotropic parameter of γ has also the same function with the foliation angle. Meanwhile, foliation orientation has a much greater influence on ε than γ for foliation angle from 45° to 90° as γε ratio increases with an increase of foliation angle. Values of dynamic elastic modulus (E), Poisson’s ratio (ν), shear modulus (μ), * Ramin Nikrouz [email protected]
1
Department of Geology, Faculty of Sciences, Urmia University, Urmia, Iran
2
Department of Mining Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
bulk modulus (K), and Lamé’s constant (λ) increase with the increase of foliation angle with the parabolic function. The results show that dynamic elastic modulus, Poisson’s ratio, shear modulus, bulk modulus, and Lamé’s constant have anisotropic behavior in relation with the foliation orientation. Keywords Foliation angle . Elastic constants . Quartz-micashicts . Thomsen’s anisotropic parameters . P- and S-wave velocities
Introduction Seismic anisotropy is being studied more frequently by researchers to enhance seismic data interpretation and petrophysical properties evaluation of the subsurface rocks. Seismic anisotropy is due to lamination, foliation, or by preferred orientation of joints and cracks and other parameters such as mineral fabric and textures. In metamorphic rocks, foliation is an important parameter to produce seismic anisotropy. Compressional (P) wave seismic data show anisotropy effects that are often difficult to attribute convincingly to anisotropy (Winterstein 1990). Shear (S) wave seismic data interpretation can also show significant influence of anisotropy (Willis et al. 1986; Winterstein 1986). P- and S-wave propagations
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