Estimation ofPcPtravel times and the depth to the core

Based on a new P velocity distribution and observed PcP travel times from nuclear explosions, the core is estimated to have a mean radius = 3477 ± 2.0 km (depth = 2894 ± 2.0 km). Five velocity models were tested for the lower-most 90 km of the mantle. The PcP data suggest that the P velocity increases slightly with depth in this region. Tables of PcP travel times have been computed for the preferred model and a core radius of 3477 km.