ELASTIC WAVE PROPAGATION IN A GRANITE AT A SCALE OF ROCK FORMING MINERAL GRAINS

Abstract

This study investigates the propagation characteristics of P-wave in granite. Specifically, the local phase velocity is evaluated experimentally using a granite plate. In the experiment, ultrasonic P-waves transmitted in the thickness direction are measured by scanning the plate surface with a laser Doppler vibrometer. The phase velocity is evaluated based on the phase delay relative to an independently measured reference signal. The phase velocity data obtained thus are processed statistically to produce probability density functions (PDF) for each rock-forming mineral species. As a result, a highly asymmetric and broad PDF is obtained for the P-wave velocity of potassium feldspar, while the PDF for quartz is found to be symmetric and much narrower. Finally, the PDFs are used to generate 2-dimensional numerical models of granite on which plane wave propagation analyses are performed. The numerical results showed that the phase velocity field perturbed according to the experimentally obtained PDFs gives a peculiar decay profile compared to the Gaussian perturbed models.