Short period (0.5–15 Hz) three component recording of the seismic wave-field of nuclear explosions and earthquakes along network of geotraverses in the continental part of Russia are used to study the structure of the upper mantle. A total of 400 mobile three component seismographs, with an average station interval of about l0 km, recorded the nuclear energy to distances of up to about 4000 km. Here we present the data obtained at the distances from 1800 to 3500 km. In despite of a range in source magnitude and profile location all record sections indicated that the offset range between 2000 and 3000 km is characterized by existence of three first arrival travel time branches with a specific kinematic and dynamic behavior. This feature has been taken as evidence for the 520 km discontinuity. P520P reflection is also clearly identified in recordings from several nuclear explosions. P-wave velocity contrast across 520-km discontinuity to be about 0.25–0.35 km/s. In addition to the 410 and 660-km discontinuities an intermediate boundary at 520–560 km depth is revealed under Siberian and East European ancient platforms, West Siberian young plates, and Urals.