Phase velocity and Q of mantle Rayleigh waves

Abstract

We analysed the long-period Rayleigh waves that were generated by the Kurile Islands earthquake (1963), its largest aftershock, the Alaskan (1964) and the Tokachi-oki (1968) earthquakes. A deconvolution technique has been successfully applied to calculate the phase velocity and Q. We found significant regional differences in Rayleigh wave Qs which are closely correlated with regional variations in phase velocity and obtained pure-path phase velocities and Q for five tectonic provinces. The Rayleigh waves suffer small attenuation along the shield region where the phase velocity is high and large attenuation over the tectonically active regions where the phase velocity is low. Applying the Q-correction to the pure-path phase velocities the regional differences in phase velocity are considerably reduced. Studies of the frequency dependence of Q by the broad-band measurements of body waves are required in order to interpret correctly surface wave dispersion and free oscillation periods. Although the Q of the model MM8 (Anderson, Ben-Menahem & Archambeau) is appropriate as an average representation of the observed Q in the period range from 200 to 300s, the differences for different great-circle paths are very large and the average Q values at periods below 200 s are lower than those of MM8.