Ultrasonic velocity anisotropy technique to enhance seismic surveys and ore prospecting

Interpretation of seismic surveys and loggings suffers from sonic velocity anisotropy in the bedrock. Locating reflectors accurately in surveys and loggings reduces the drilling in ore exploration. Hence it is important to determine the sound velocity anisotropy in core samples. Uniaxial time-of-flight measurements were carried out under low pressure (10 kPa) for the X, Y, and Z directions independently. We measured (N=11) cubic (25 mm) rock samples. The longitudinal wave velocities were obtained with 1-8 MHz broadband transducers. We also present an ultrasonic triaxial anvil setup for measuring longitudinal (Vp) and shear wave (Vs with 0° and 90° polarizations) velocities of cubic rock samples under crustal-pressures (up to 300 MPa) in three directions. Our results from a selection of Finnish Precambrian rocks show ultrasonic velocities in the range of 2990-6800 m/s and velocity anisotropies reaching from 2% to 26% at low pressure.