| Abstract: | P- and S-wave velocities in nepheline basalt, Hamada, as well as diabase, Maryland, were measured experimentally to 1000°C and 2.5 GPa. A remarkable frequency dependence of large velocity-decrease was observed for both P- and S-waves at temperatures above 500°C. Remarkable velocity-characteristics, which cannot be explained by the existing theories, were: 1. (1) Velocities were decreased considerably at 1–3 MHz. Above 3 MHz, samples showed elastic behavior like that of a perfect solid, and below 1 MHz, velocity-decrease decayed gradually. 2. (2) Both P- and S-wave velocities decreased in the same way and almost to the same degree. 3. (3) The higher the temperature, the more remarkably velocities decreased, at least up to the experimental limit temperature. A hypothesis of the relaxation of stress waves by the fluid-flow in the inclusions is proposed. Examples of geophysical applications are given for the attenuation and travel-time anomalies in the volcanic region and the P- and S-wave velocity-decrease in the upper mantle beneath continents. |
