Attenuation of Long-period P-waves and Q in the Mantle

Abstract

Several attempts have been made to determine a Q distribution in the mantle using the amplitude ratio of multiply reflected core phases or the diminution of body wave amplitudes with an increase in epicentral distance. When seismic waves travel in an anelastic medium like the earth, it is expected that not only the amplitudes of the waves diminish but also their periods will lengthen. In the present study, the spectral analysis of long-period P-waves from an intermediate earthquake has revealed the phenomenon that the spectral peak with a period of about 10 seconds moves toward longer period side with the increase in epicentral distance. Records of vertical component obtained at 23 stations with epicentral distances from about 37 to 105 degrees were used in the analysis. By comparing this phenomenon with the transition of the maximum spectral peak expected from a theoretical model, a Q distribution in the mantle has been tentatively estimated.