DENSITY INHOMOGENEITIES OF THE UPPER-MANTLE OF THE CENTRAL BALKANS

A 3-D density model was created for the Central Balkans area down to a depth of 670 km on the basis of seismic (both artificial sources and earthquakes) and gravity data. This model is based on density columns constructed for the main geological units of the study region. The den sities for these columns were obtained using the density variation met hod. This method makes it possible to extrapolate the density distribu tion from the well-studied uppermost layers to the deeper levels of th e Earth. The constructed 3-D density model was interpreted in relation to the available data on the heat flow and the seismicity of the regi on. The subdivision of the region by the Maritza fault into two parts- the southern part including the Rhodope massif and the northern part i ncluding the structures of Alpine activation of Srednogorie and the Ba lkanides-was confirmed. The upraised position of the 400 km boundary w ithin the upper mantle, which was established from the density modelli ng, is assumed to be a sign of development of recent geodynamical proc esses over the Srednogorie block, From the viewpoint of seismicity pre diction, a finding of mantle inhomogeneities orthogonal to the Maritza suture is of great importance.