PKIKP and Pseudo‐PKIKP Phases at distances of less than 140°

Abstract

In several attempts to establish from observations the travel‐time curve for PKIKP (called P′ or P″ by some authors) the beginning of this curve has been drawn with a relatively strong curvature corresponding to a decrease of dt/dθ from roughly 4 s/deg atθ= 110° to about 2 s/deg at 130°. Apparently, travel times of different wave types had been combined. Actually, the observed travel‐time curve of PKIKP is nearly a straight line in agreement with calculations. Near an epi‐central distance of 115° the amplitudes of PKIKP increase by a factor of roughly 5. This probably indicates the transition from the diffracted to the direct PKIKP. The portions of the travel‐time curves with a slope corresponding to dt/dO near 4 s/deg which erroneously had been attributed to PKIKP belong to several wave types which seem to follow P, pP and sP or precede PP, each at roughly constant time intervals. Among causes for such multiplicity of phases are effects of irregularities in the Earth, of discontinuities and of diffraction. Copyright © 1960, Wiley Blackwell. All rights reserved