Open AccessDiffraction by Anomalous Regions in the Earth's Mantle
Author(s) -
Woodhouse J. H.
Publication year - 1973
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1973.tb05833.x
Subject(s) - diffraction , discontinuity (linguistics) , mantle (geology) , amplitude , dissipative system , physics , geophysics , geology , optics , mathematical analysis , mathematics , thermodynamics
Summary Asymptotic results are derived for the travel times and amplitudes of waves diffracted by surfaces of discontinuity in the Earth's mantle. A canonical problem, defined to be that of diffraction by a uniform elastic or visco‐elastic sphere in a uniform elastic medium, is first solved asymptotically and the result applied, by means of simple ray theory, to an Earth model which is spherically symmetric except for the diffracting discontinuity. Some calculations are carried out for comparison with the signals from the Bukhara explosion discussed by Douglas et al. and an attempt is made to identify their arrival P H 1 with a diffracted arrival from a mantle discontinuity. To explain the low amplitude of the direct wave a dissipative region in the mantle, which is avoided by the diffracted wave, is postulated and the approximate values of Q needed to equate the amplitudes of direct and diffracted waves are calculated.