The Density Jump at the Inner Core Boundary in the Eastern and Western Hemispheres

Abstract

The results of analysis of more than 1300 new PKiKP/PcP amplitude ratios measured in Southeast Asia and South America at the epicentral distances of 3.2°–35.2° are presented. The density jump in the Eastern Hemisphere of the Earth’s inner core (IC) is 0.3 g/cm³, and it is 0.9 g/cm³ in the Western one. Taking the large discrepancy in the obtained estimates into consideration, maintenance of such large lateral variations in the mosaic properties of the IC reflecting surface requires considerable variations in the thermodynamic parameters (mostly temperature) of the inner–outer core transition. However, if the observed asymmetry in the density jump distribution is of a global character, the data presented support the translation model of the IC dynamics. This model implies IC crystallization in the Western Hemisphere and melting in the Eastern one, not vice versa, as suggested by another geodynamic model based on thermochemical convection in the outer core and the thermal balance of the core–mantle system.