PKKP, P′P′, and the Earth's core

Abstract

Observed times and amplitudes of PKKP and P′P′ are discussed. At distances between 100° and 120° PPP with angular distances over 180° precedes P′P′ by less than one minute and has occasionally been confused with P′P′. The travel-time curve for longitudinal waves between points on the surface of the core is revised. Observed amplitudes of short-period waves in P′ and PKKP are roughly four times greater than the amplitudes calculated on the assumption that the distribution of energy as a function of period is the same for waves through the core as for those through the mantle only (P, PP, and S). PKKP waves with periods of more than three seconds are very rare. PKKP through the inner core is usually not observed, in agreement with, theoretical expectation. The fact that PKKP through the outer part of the core is well observed indicates a ratio of probably at least 1.7 for the densities inside and outside the outer core unless the ratio is near 1.0. At the boundary of the inner core (radius about 1300 km) the velocity increases from 10± to 11± km/sec within 100±km and is 11.2± km/sec in most of the inner core. P″ at distances between its beginning near 105° and a distance of about 125° is probably mainly due to waves reflected at the inner core.

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