The structure of the uppermost 100 km 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.

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It has been shown that accurate predictions of compressional and shear‐wave velocities can be derived from measurements of clay content, porosity, and bulk density. In this paper, we test the efficacy of using a sequence of established petrophysical formulations to go a step further and predict porosity and bulk density as well as velocity from clay content alone. Other variables, like grain and pore‐fluid properties, are assumed to be constant, while empirical relationships are used to model such behaviors as grain packing and compaction. The sequence of formulations, referred to as the “model,” is evaluated using well‐log and core data from the Amazon Fan collected during Ocean Drilling Program Leg 155. Clay contents are estimated from the borehole gamma‐ray logs. These are input to the model, which in turn predicts observed porosities to a rms error of <20%, and bulk densities and compressional velocities to rms errors of ≤10%. The results suggest that with better measurements of clay content and improvements to the model, even more accurate predictions of velocity might be achieved for unconsolidated sediments.