Measurements of Elastic Wave Velocities in Rocks at High Temperatures. I

Abstract

A new method of measurement of elastic wave velocity in rocks at high temperatures by means of ultrasonic impulse transmission is presented. This method consists in directly measuring the wave velocity by making use of piezoelectricity of β-quartz crystal. It is shown that pieces of this crystal cut in several orientations can be used as transducers which receive and send out the longitudinal, transversal, or both types of waves. In our experimental conditions, β-quartz did not change in phase to α-tridymite at 870°C, presumably due to the inversion being of a sluggish type. The efficiencies of transducers were not reduced at 870°C and the measurement could be made up to about 1000°C or higher. From this fact, the possibility of the direct measurements up to several hundreds degrees above 1000°C is suggested.
Rock specimens were cut out from volcanic rocks which were collected from several locations; Mihara Volcano, Ooshima Island; Usu Volcano and Showa-shinzan, Hokkaido; Hakone, Kanagawa Prefecture; Shidara, Aichi Prefecture.
Some of the results obtained by this method are described; (1) the variation of longitudinal and transversal wave velocity with temperature; the increase of wave velocity with the rise in temperature; (2) the new volcanic rocks recently erupted showing the tendency of this increase of elasticity; (3) the increase of Poisson's ratio with the rise in temperature.