ATTENUATION OF SHEAR WAVES IN THE UPPER MANTLE BENEATH THE SEA OF JAPAN

Abstract

ScS and sScS phases recorded by the long-period seismographs are analyzed to study the attenuation of shear waves in the upper mantle beneath the Sea of Japan. Data from the Vladivostok deep-focus earthquake of September 10, 1973 are used. The value of Q_β', the average Q_β for the mantle above the hypocenter (depth=552km), is about 70 for the frequency range of 0.02-0.07cps. This value is lower than those of some of previous estimates in and around the Japanese region, but is consistent with Q_R, Q of Rayleigh waves, for the trench and marginal sea region obtained from the "pure-path" analysis of long-period (T=200-300sec) Rayleigh waves. It is emphasized that the signal-to-noise ratios should be taken into account to obtain an unbiased estimate of Q.