Pwave diffraction theory and the structure of the core-mantle boundary

Abstract

The theory for diffraction of elastic waves in a spherical geometry is reviewed and modified to apply to a multilayer geometry. We have made numerical calculations of the attenuation function for P waves in the shadow of the core for certain basic geometries and for models which have a single layer at the core‐mantle boundary. Resonance phenomena due to the presence of the layer are discussed, and an attempt is made to explain observed peaks in the attenuation spectrum for various regions of the core boundary. A region between 30 and 160 km thick, with a reduced shear velocity and an increased density, appears to be the most likely explanation of the data.

Model Study on Core-Mantle Boundary Structure

“…18 showed discrepancy with the results of the theoretical computation by Phinney and Alexander (1966). anelasticity.…”

“…By taking these units, the difference in the scale factors is erased. In this figure Phinney-(numeral) means the cases treated by Phinney and Alexander (1966). Phinney-1 is a reference earth model having homogenous mantle and core.…”

“…(Watson, 1918;Bremmer, 1949;Takeuchi, 1950;Scholte, 1956;Nagase, 1956;Duwalo and Jacobs, 1956;Knopoff and Gilbert, 1961;Rubinow and Keller, 1961;Nussenzweig, 1965;Phinney and Alexander, 1966;etc. ) Recently extensive studies were intended by several authors.…”

“…Although this kind of methed to enhance the accuracy of results has not been attempted as yet, this method is highly powerful in the present study, in which materials having rather high attenuation are used in order to make continuous velocity gradients over a wide frequency range of waves. Attenuation functions are obtained by formulae which are essentially the same as those of Phinney and Alexander (1966) sional numeral, ha. By taking these units, the difference in the scale factors is erased.…”

“…Waves diffracted by the core were also utilized for the study of the core-mantle boundary. Alexander and Phinney (1966) and Phinney and Alexander (1966) The first method is aimed to study Q values in the bottom part of the mantle by taking spectral ratio of the direct waves observed at different stations.…”