A 22 degrees long seismic profile for the study of the top of D"

We present a collection of 100 vertical component seismograms of a Kuril Is lands earthquake recorded by stations in western Europe (between 73 and 95 degrees of epicentral distance) which shows evidence of a PdP wave reflecte d on top of D " beneath northern Siberia. The PdP travel time curve varies rapidly, suggesting the existence of sharp lateral variations (scale length smaller than 1 degrees). The first onset times observed at distances large r than 85 degrees are compatible with a D " velocity about 1% larger than s tandard models along these paths, up to a depth of 2850 km. By one dimensio nal forward modeling we find one model with a 2.8% discontinuity at 2605 km depth, another with a 7 km thick 3% low velocity lamella at 2607 km depth. They both generate waveforms which fit the data similarly.