Differential PcP Travel Times and the Radius of the Core

Backus-Gilbert inversions of a new differential PcP data set result in estimates of the core radius, 3484–3486 km, compatible with those obtained from the inversion of large sets of normal mode data. For that part of the core sampled by the data, undulations in the core-mantle boundary can be of order no more than 5–10 km, in the worst possible case. Signal misidentification and lateral inhomogeneities in the upper mantle must be accounted for in observed short-period differential PcP travel times. In the case of Amchitka data, seismic ray tracing is used to describe the effects of a dipping lithospheric plate beneath the Island.