Great-circle Rayleigh wave attenuation and group velocity, Part II: Observations for periods between 50 and 200 seconds for nine great-circle paths and global averages for periods of 50 to 600 seconds

Abstract

Great-circle group velocities and attenuation coefficients for the period range 50 to 200 s have been determined for Rayleigh waves from three Kurile Islands earthquakes ranging from magnitude 6.6 to 7.2. These data have been combined with earlier data from Mills and Hales to produce global average group velocities and attenuation coefficients for periods between 50 and 600 s. Global average phase velocities have been determined by integrating global average group velocities for periods from 50 to 340 s. Equivalent fundamental mode periods from 0S 34 to 0S 168 (60–240 s) are calculated and corrected for dispersion due to anelasticity. Comparison of group velocities and equivalent spheroidal mode periods with those calculated for recent earth models shows that shear velocities in the upper mantles of those models are too high to fit our data. Global average Q′s for Rayleigh waves are slightly lower (approximately one standard deviation at most periods) than those predicted by model MM8 of Anderson, Ben-Menahem and Archambeau. Attenuation coefficients at short periods (50–100 s) agree well with similar measurements for oceanic and continental paths.