DiffractedP-wave studies of the Earth's core: 2. Lower mantle velocity, core size, lower mantle structure

Preliminary travel times of diffracted P waves have been determined to distances of 167° and found to have an apparent velocity at the surface of 24.55±0.08 km/sec, rather than the Jeffreys-Bullen value of 25 km/sec. The diffracted wave velocity has been used with Jeffreys' solution of the Herglotz-Wiechert equation (giving the velocity structure of the mantle) to determine a core size of 3537±9 km and a lower mantle velocity of 13.64±0.045 km/sec. These values are shown to be consistent with a shadow boundary determination of 96°, established by different methods in an earlier study. The dispersion is less than 1% over a 25- to 2.5-sec period range, suggesting absence of structure at the base of the mantle. There is, however, suggestion of circumferential irregularity at the core-mantle interface.