Regional variations in the uppermost 100 km of the Earth's inner core

Abstract

The structure of the uppermost 100km of the inner core was examined from PKIKP and PKiKP waveforms in the distance range of 118°-140°. We found evidence of a low-velocity layer in the uppermost inner core in the equatorial region predominantly located between longitude 20°W to 140°E. In the latitudinal direction the anomaly is detectable from 35°S beneath the Indian Ocean to 60°N underneath Asia. The maximum thickness of the low-velocity layer inferred from waveform modeling is 40 km with velocity jump of about 3%. We speculate that this layer may represent newly solidified core in the area where vigorous compositional convection in the outer core coincides with new crystal growth in the inner core. Copyright 2004 by the American Geophysical Union.