<p>Based on data from nuclear explosions along the Quartz profile, which crosses the Pre-Ural trough with the Urals and the West Siberian plate and is part of the Altai-Sayan fold region to the southeast, the structure of the lithospheric mantle and asthenosphere has been studied. A two-dimensional seismic model of the upper mantle has been constructed using the ray tracing method of the propagation of refracted–refracted and reflected longitudinal waves in a directly spherical approximation of the Earth’s shape. Regional structural-velocity heterogeneities of the two-layer mantle lithosphere with decreasing thickness toward the fold region and correspondingly increasing thickness of the asthenosphere were discovered. Particular attention is drawn to localization of a mantle heterogeneity corresponding to the location of the Koltogorsk–Urengoy rift graben. The distribution of residual mantle Bouguer gravity anomalies (recalculated to the base of the earth’s crust) shows a clear zoning corresponding to seismic inhomogeneities with a weak dependence on the Moho depth.</p>