Detection of PKJKP at intermediate periods by progressive multi-channel correlation

Abstract

We have identified the seismic phase PKJKP, traveling through the inner core of the Earth as a shear wave, in intermediate-period (2–10 s) records of the deep 1996 Flores Sea earthquake at eight stations of the French seismic network. This constitutes direct evidence of the solidity of the inner core which, while generally recognized, was until now only inferred from indirect evidence. The arrival times on stacked seismograms require a shear-wave velocity at the top of the inner core β ICB=3.65 km/s in agreement with values suggested from normal mode observations. Julian et al.'s 1972 observation of a lower velocity (2.95 km/s) is easily reconciled with our result if interpreted as the surface reflection pPKJKP. The high Poisson ratio ( ν=0.44) can be reconciled with a normal crystalline structure without invoking partial melting on account of the overwhelming pressure at the center of the Earth.