Attenuation of Seismic Body Waves in the Mantle

Abstract

Summary The attenuation of seismic body waves is a direct measure of the absorption due to nonelastic processes within the Earth. Accurate amplitude decrement data for seismic body waves require the measurement of the spatial decay rate along a given ray, but measurements are restricted to the surface of the Earth. Recent studies have shown that the average Q for shear, throughout the mantle is about 600 and that the average Q for the upper 600 km of the mantle is an order of magnitude less than the rest of the mantle. Spectral amplitude comparison of the seismic phases SKS and SKP with common paths in the mantle and core allows the Q, for compression, in the mantle to be estimated. Preliminary results indicate that the Q for compression is at least 2.5 times that for shear.