Velocity Anisotropy Of Two Deep Crystalline Samples

Abstract

Using ultrasonic velocity measurements taken over a multiplicity of directions we show that samples exhibit weak to moderate anisotropy of seismic velocities. We further define the anisotropic geometry with high resolution scanning electron microscopy. Our data indicate that one sample, a granite, is transversely anisotropic, and that the presence of fine to moderately fine microcracks is the most important factor effecting the velocities. We model the angular velocity dependence using 5 elastic constants and show that all 9 observed velocities fit these predictions to within 0.1 km/s. We are unable to obtain similar fits to a second sample, a mica-schist, in the same fashion. SEM observations indicate this rock displays orthorhombic symmetry. We made additional velocity measurements in order to calculate 9 elastic constants, and found that the predicted angular velocity dependence agreed much better with our velocity observations.