On the lack of seismic discontinuities within the inner core

Abstract

Recent work has suggested that seismic discontinuities might exist within the inner core (IC). Such boundaries could be caused by changes in the strength and orientation of anisotropy, by variations in the fraction of partial melt or by a solid-solid phase transition involving iron. In this work, we search for evidence of IC discontinuities with reflection seismology techniques that use precritical PKiKP waveforms as empirical source pulses. Because any phase reflected from an IC discontinuity will have a small amplitude, we develop a technique combining source and receiver stacks in the search. We perform resolution tests where we compare the data with synthetic waveform stacks created using generalized ray theory and appropriate attenuation operators. Our results show that the IC lacks a significant (impedance jump > 3 per cent), sharp (thickness <3-4 km), global discontinuity to depths of 800 km below the boundary with the outer core. © 2005 RAS.