Travel times from 16 events recorded at two temporary networks of short-period seismometers deployed across Australia have been used to study the P wave velocity structure of the mantle below depths of 1700 km. The slowness-distance curve derived from these times shows small deviations from the slownesses predicted from the preliminary reference earth model of Dziewonski and Anderson <1981> that may be significant. The most important feature is a rapid decrease of more than 0.5 s/degree between distances of 85¿ and 88¿. Velocity filtering of seismograms from 5 nuclear explosions in Kazakh recorded at these Australian networks indicates the presence of two arrival branches at distances between 83¿ and 91¿ whose slownesses differ by 0.40 to 0.55 s/degree and which intersect at a distance of 87¿. Processed P wave seismograms from the Yellowknife array in Canada also indicate the presence of a similar phenomenon in the same distance range in two separate regions. The results can be explained by a widespread rapid or sharp increase in velocity of 2.5 to 3.0% about 200 km above the core mantle boundary.