Caustics Produced by Waves Through the Earth's Core

Summary Caustics produced by SKP, PKS, PKP and other phases through the Earth's core are investigated. No impulses from diffracted waves with periods of two seconds or more have been found beyond five degrees from caustics. Short waves preceding the main PKIKP-phase at distances between 125° and 140° probably have their deepest point in or near a transition zone between the liquid outer and the probably solid inner core and it is unlikely that they are related to the caustic of PKP near 145° although their travel-time curves end near this caustic. The observed range of long-period waves diffracted beyond the caustics of several phases is smaller than the maximum range calculated by Jeffreys.