The detection of PKIIKP and damping in the inner core

Abstract

SUMMARY - The phase PKIIKP, reflected once from the lower surface of the<br />inner core boundary, was most probably recorded by LAS A from the Faultless<br />underground nuclear explosion at 10°.9 angular distance. The array beam detected<br />a P onset, with the correct slowness, within 2 sees of the theoretical travel time.<br />The ground amplitude is 3 + 1 millimicrons at a dominant period of 1.5 sec.<br />By comparison, the PKiKP ground amplitude from Faultless is 75 millimicrons<br />at a dominant period of 1.1 sec.<br />This detection again confirms the sharpness of the inner core boundary<br />and the 1968 core travel times for PKiKP. The additional attenuation of<br />PKIIKP over PKiKP yields, from direct and spectral measurements, Q = 4 5 0 + 1 00<br />for P waves in the inner core. This value sharpens the earlier estimates of I.<br />Sacks, G. Buchbinder, A. Qamar, and A. Eisenberg and is almost independent<br />of core structure and rigidity.<br />On the assumption of a constant velocity in the inner core, the observed<br />differential PKIIKP minus PKiKP travel time requires an average P velocity<br />of 11.4 + 0.02 km/sec for an inner core radius of 1216 km.