Geophysical Journal | 2008 volume 30 5

Three-dimensional P-velocity model of the Black Sea

© Gobarenko V.S., Egorova T.P.

The structure of the upper mantle of the Black Sea has been studied from the residuals of P-wave arrivals along the traces crossing the Black Sea using the method of local seismic tomography based on Baikus-Gilbert approximation. The parameters of foci of earthquakes, occurred in the Black Sea and its surroundings, and localization of earthquake parameters have been studied. For calculation of velocity corrections we used the time arrivals for 1378 phases of Pn waves from 88 earthquakes within the Black Sea region recorded by seismic stations located around the Black Sea. Derived distribution of P-wave velocities is represented by a set of horizontal sections at the depth of 40?55 km and two vertical cross-sections. According to its velocity structure, the most complicated and ambiguous area is one located within the central part of the Black Sea. A NW-trended chain of high-velocity anomalies in the central part of the Black Sea, which turns eastwards into contrast gradient zone, marks the position of Odessa-Sinop (Trans-Black Sea) fault. The West and East Black Sea depressions are specified by increased values of velocities but differ by configuration and alteration with depth. The lithosphere of the West-Black Sea Basin is characterized in general by higher velocities increased with depth, whereas below the East-Black Sea Basin a density decrease has been detected at the depth of 70-80 km, which points out at the presence of inversion zone here. Different velocity structure of the lithosphere below two basins of the Black Sea relates, probably, with diffrent thickness of the lithosphere and can be explained by their origination on different microplates of different affinity and by the peculiarities of rift and post-rift phases of evolution.

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