Velocity and Q of mantle waves

Phase velocity and Q of long-period waves have been determined for 13 great-circle paths for Rayleigh waves and 12 great-circle paths for Love waves. Group velocities are also determined by band-pass filtering technique. Some of the preexisting data are incorporated to obtain representative sets of data for Q, phase and group velocities. With these sets of data stringent tests of various Earth models are possible. Each great-circle path is divided into oceanic, “tectonic” and shield portions, and a regression analysis is made on the phase velocity data to obtain pure-path dispersion curves for these distinct tectonic provinces. For both Love and Rayleigh waves, the pure-path phase velocity is found to be significantly lower for tectonically active regions than for ocean and shield. This difference in the phase velocity curve suggests that the mantle structure beneath tectonically active regions is significantly different from that elsewhere even at depths below 200 km