Attenuation in the Mantle and Rigidity of the Core From Multiply Reflected Core Phases

Abstract

In 1956 Press reported on single and double reflections of shear waves at near normal incidence from the earth's core and was able to estimate the average dissipation constant of shear waves in the mantle and place an upper bound for the rigidity of the earth's outer core at the core-mantle boundary. However, because of excessive reverberations and the low sensitivity of the seismographs only a few usable seismograms were found in five years of continuous data. In this paper me report on a seismogram showing unusually clear, near-vertical multiple reflections of shear waves from the earth's core. We have been able further to reduce the upper bound on the rigidity of the core, to estimate the average dissipation coefficient for 20-30 sec shear waves in the mantle, and to estimate the dissipation in the regions of the mantle above and below the earthquake focus. In addition, we have recomputed the origin time and depth of focus from information contained in this single seismogram.