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

We have identified the seismic phase PKJKP, traveling through the inner cor e 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 cor e which, while generally recognized, was until now only inferred from indir ect evidence. The arrival times on stacked seismograms require a shear-wave velocity at the top of the inner core B-ICB = 3.65 km/s in agreement with values suggested from normal mode observations. Julian et al.'s 1972 observ ation 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 (v = 0.44) can be reconciled with a normal crystalline structure without invok ing partial melting on account of the overwhelming pressure at the center o f the Earth. (C) 1998 Elsevier Science B.V. All rights reserved.