SEISMIC TOMOGRAPHY MODEL OF EARTH CRUST OF SW BULGARIA AND SURROUNDINGS

The paper deals with the tomography investigations of the earth’s crust inhomogeneity of the SW Bulgarian area and its geodynamic features. The main aim is to reveal the relationships of the seismic tomography model and the crustal inhomogeneity’s structures located at SW Bulgaria and surroundings. This aim is strongly related with the seismic activity of the region, where strong earthquakes in Kresna-Kroupnik (M7.2 and M7.8, 1904), Valandovo (M6.7, 1931) and Skopje (M6.1, 1963) with a lot of destructions and victims occurred. There are also other less active seismic sources as Velingrad, Mesta, Struma, etc. with lower seismic potential. The seismic tomography model, calculating the velocity residuals for P and S seismic waves from the optimal velocity model helped to establish the possible reasons for the geodynamic features of the region. Discovered velocity anomalies coincide pretty well with the previously investigated geophysical anomalies (velocities’ depth changes, asthenosphere gradients, thermal conductivity, fluids saturation, etc.) and geodynamic features (fracturing, faults, grabens and horsts, crustal movements, etc. The local seismicity is also considered, showing higher concentrations of hypocenter near the established velocity gradient areas. The performed tests about the accuracy of the calculations and ongoing interpretation helped to increase the reliability of the results obtained.