The earthquake P phases which penetrate the earth's core

Abstract

Travel times of all earthquake phases which enter the core as P and emerge as P are explained in terms of a core model containing two velocity discontinuities. Amplitudes of PKIKP and PKP change little with changes in distance from the source except in the rangeΔ = 142° to Δ = 152°. In this range large amplitubes are observed which result from the simultaneous arrival of two phases as well as large amplitudes which represent the PKP₁ - PKP₂ caustic. Amplitudes in the caustic allow detection of events perhaps smaller than magnitude 4. In all distance ranges PKIKP and PKP are useful in magnitude determination, but added care must be taken if they are used in the distance range where amplitudes are large. Magnitudes determined from PKIKP and PKP are very consistent as are focal depths. The PKJKP phase is small if present at all.