Scattering of Seismic Body Waves by Small Random Inhomogeneities in the Earth
Scientific rept. on Phase 3
ROYAL NORWEGIAN COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH KJELLER
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A theory of scattering of seismic body waves by small random spacial fluctuations in density and elastic parameters in an otherwise spherically symmetrical earth model is developed. It is shown that a primary wave disturbance of either P or S type travelling through a slightly irregular solid medium will generate scattered waves of both P and S types. Explicit formulae are derived for the mean square amplitudes of P waves scattered from several different assumed forms of primary P wave. The theory assumes that the primary wave may be locally approximated by a plane wave inside each part of the scattering region whose size is comparable with the mean size of the irregularities present and that ordinary ray theory may be applied to calculate the travel times and amplitudes of both primary and scattered waves. The theory supports the writers earlier suggestion that observed precursors to the seismic core phase PKIKP may originate by scattering from the phases PKP1 and PKP2 by irregularities in the vicinity of the earths mantle-core boundary.