Upper Crustal Velocity Model for the Southeastern Boundary of the Siberian Platform

—Based on the common-mid-point (CMP) seismic data on the 3-DV reference profile, using dynamic conversion of refracted waves into time sections, we constructed velocity sections across four crustal blocks in the boundary region of ​​the Siberian platform and the folded region: the Nizhnealdansakaya (Lower Aldan) depression, Pre-Verkhoyansk foredeep, Sette-Daban block, and West-Verkhoyansk folded area. The four structures contact each other along the fault zones with the velocity model abruptly changing at these boundaries. Within the Lower Aldan depression, the topography of two refractive discontinuities is constructed: the basement boundary and intermediate boundary in the sedimentary cover. In the Pre-Verkhoyansk foredeep, one refractive discontinuity is revealed in the sedimentary cover, whereas the basement boundary in this region is located at greater depths than covered by the observation system. All the discontinuities established in these blocks are lithological. In the uppermost crust of the Sette-Daban block and West Verkhoyansk folded area, gently sloping refractive boundaries with velocity jump and steep velocity gradients directed towards the underlying medium are detected. The Sette-Daban block has especially high seismic velocities. The refractive boundaries in these blocks are not lithological.