Home – Home – Jornals – Russian Geology and Geophysics 2006 number 5

Several long-range profiles were shot with nuclear explosions within the Siberian Platform. The seismic records of both chemical- and nuclear-explosion profiles have revealed new peculiarities of the upper-mantle structure in the region. Seismic sections were constructed by ray tracing. To build the most informative starting model, the τ   (V,  x) method was applied, which implies construction of τ-time sections using the refraction and wide-angle reflection travel times for several velocity lines V = const. The modeling has revealed abnormally high (up to 8.4-8.5 km/s) upper-mantle velocities beneath the ancient Siberian Platform and low ones beneath the young West Siberian Plate. The upper mantle is shown to be of layered structure, with reflecting boundaries at depths of about 100, 150, 240, and 320 km. The boundary N1 at depths of 70-120 km is the most persistent; it often underlies low-velocity zones. The existence of velocity inversion zones and reflecting boundaries might be accounted for by fluid concentration at particular depths of the lithosphere, which suggests its rheological layering. The asthenosphere-lithosphere boundary has not been recognized in the velocity cross-sections.