FREQUENCY-DEPENDENT-Q IN THE EARTHS OUTER CORE FROM SHORT-PERIOD P4KPPCP SPECTRAL RATIO/

The attenuation of P-waves and its frequency dependence in the Earth's outer core are investigated using the P4KP/PcP spectral amplitude rat io. We analyze PcP and P4KP phases recorded on short-period seismograp hs in the Japan Islands for three large intermediate-depth and deep ea rthquakes from March 1991 through July 1994. The observed P4KP/PcP spe ctral amplitude ratio is corrected for responses of the mantle and the core, and attenuation in the lower mantle. The responses for P4KP and PcP are considered for the frequency dependence of their reflection/t ransmission coefficients at the core-mantle boundary. After the correc tions, we estimate Q(p) values in the outer core in the frequency rang e of 0.15-2 Hz, and find that the Q(p) increases with increasing frequ ency (f) in the form of Q(p)=(4,609 +/- 100) f((0.55 +/- 0.07)). Th, o bserved frequency-dependent Q(p) values increase more slowly with incr easing frequency than those predicted by the model of the bulk attenua tion based on the relaxation mechanism of immiscible particles in the outer core.