Review on the Seismological Structure of the Earth's Core Inferred from Body-wave Core Phases

The present paper reviews recent studies on the seismological structure in the Earth's core inferred from analyses of seismic body waves. Based on the recent interpretations on the precursors to the PKIKP and the analyses of the PKP waveforms at distance range from 125 to 150 degrees, it is generally accepted that there is no transition layer (F zone) between the inner core and the outer core. It is supported by the rusults of the extremal bounds on the P wave velocity which were also evaluated using the τ-method and the linear programming method. The anelasticity in the outer core is very small, but that in the inner core is very large, especially at the upper part of the inner core, where the process of the solidification is thought to be occurring. The velocity structure in the outer core is homogeneous and isotropic, whereas that in the inner core may be heterogeneous and/or anisotropic. Using the travel time anomalies from ISC bulletines, the hypothesis that the velocity in the inner core may be faster in the N-S direction than that in the E-W direction, has been proposed. The core-mantle boundary topography is obtained by inverting arrival time data of PcP, PKP and PKKP. The CMB topography estimated from PKKP is smoother than that from PcP and PKP.