Use of ultrasonic interferometry technique for studying elastic properties of rocks

This communication reports data on the elastic properties of a specimen of obsidian taken by the pulse superposition method and is the first example of the successful application of this method to a natural rock material. Birch and his associates [Birch, 1960; Birch and Bancroft, 1938a, 1938b, 1942; Birch and Dow, 1936] found an anomalous behavior with pressure and temperature for some glasses, particularly obsidian, in that the sound velocity decreases with pressure and increases with temperature. A further anomaly is noted, since the compressibility of these silica-rich glasses increases with pressure (Bridgman, 1924, 1925, 1939, 1948). Because of the extreme sensitivity of the pulse superposition method (Schreiber and Anderson, 1966), one should be able to determine the extent of anomalous behavior, using experiments in a limited pressure.