The main features of the interface between the crust and the upper mantle in the Middle Urals (in the vicinity of the deep drillhole SC-4)

Analysis of both P- and S-wave seismic data from the Middle Urals supports the existence of a multi-layered crust-mantle transition zone and a deep crustal root along the central axis of the Urals, Data from deep seismic sounding (DSS) nuclear explosions (Rubin I and Quartz), quarry blasts from industrial sources, and wide-angle experiments (Krasnouralsky and UWARS) are integrated to form the basis for this study. The crust-mantle transitional complex begins in the eastern par? of the Pre-Uralian foredeep where it consists of relatively thin layers (thickness similar to 3-5 km) with alternating high- and low-velocity layers. Toward the axis of the Urals the transition zone thickens to 10-15 km beneath the Tagil are before thinning toward the East Uralian zone. The average interval P wave velocity for the transition zone varies from 7.3-7.8 km/s. The thickness of the crust is found to reach a maximum of 55-60 km in the vicinity of the super deep borehole SG4. In the area of SG-4, the Moho shallows from the Tagil zone west to the Central Urals uplift and Western Urals fold zone. The upper mantle is characterized by a nearly uniform velocity of 8.5 km/s.