Travel time analysis of P waves arising from six underground nuclear explosion at Novaya Zemlya

SUMMARY. - The analysis of the travel times of the P waves generated bysix underground nuclear explosions in Novaya Zemlya shows notable earlyarrivals (oo4sec) at the Fennoscandia stations. These observations, togetherwith a marked linear dependence of the travel times on the epicentral distancethroughout the interval 8.5 < / J ° < 20.4. were evaluated with the aim of producinga satisfactory model for the upper mantle of the Baltic zone. In particular,there appears a considerable mantle zone with almost uniform velocity, or atleast, with not of increasing velocity. This mantle zone is delimited above by adiscontinuity at the 86 km depth (v = 8.45 km/sec), and delimited below by the«20° discontinuity» (h = 507 km; v = 10.56 km/sec).The proposed model is amply verified on the basis of the foreseen traveltimes compared with the corresponding ones, observed from a fair number ofimpulses associated with teleseismic Pn, noticeable as far as 40°, and from phasesreflected and refracted on the discontinuity at 507 km