On the observation of high frequency PKiKP and its coda in Australia

The seismic phase PKiKP, reflected from the inner core, and its coda give information on the short scale heterogeneities at and below the inner core boundary (ICB) of the Earth. We have collected PKiKP recorded at short distances (<45°) at broadband stations in Australia and at the Warramunga seismic array (WRA). Despite potential complications from a dual-passage through D″, PKiKP is frequently observed on single traces in the frequency band 1-5 Hz. PKiKP usually has a sharp onset, but sometimes its waveforms have multiple pulses separated by times of the order of 1 s. At WRA, the coda of PKiKP initially decays very rapidly after the main pulse. Thereafter, its amplitude is nearly constant and more than three times smaller than PKiKP with duration longer than 200 s. Our observations differ from those of [Nature 404 (2000) 273-275], at rather greater distances, who found that the coda is larger than PKiKP and increases slowly. We suggest that the PKiKP coda is generated near the inner core boundary by complex reverberation effects, rather than scattering through the volume of the inner core.