Ultrasonic measurements of S waves using laser interferometry

Abstract

We present laboratory measurements of ultrasonic S waves in Bentheim sandstone using laser Doppler interferometry (LDI). S wave velocities and polarizations (along with those of P waves) are important in the characterization of elastic wave anisotropy. LDI facilitates this by measuring the waves velocities and vector of particle displacements (polarizations) on the surface of a sample. With a sufficient number of measurements, the complete elastic stiffness tensor of the material can be calculated. Anisotropy can be caused by mineral orientation or by rock fabric and can also be induced by the application of non-hydrostatic stress. In this work we show that S wave polarization is measurable with the LDI technique and also that we can track changes in polarization due to applied stress.