BODY-WAVE VELOCITIES IN THE CIRCUM-ADRIATIC REGION

The paper presents body-wave velocities in the crust and upper mantle of the circum-Adriatic region obtained by analyzing travel times of regional phases of 419 selected earthquakes with epicenters in the central part of the External Dinarides. The studied region was divided into five areas and two kinds of velocity models were determined for each of them. The first kind (inter-area models) gives average velocities that characterize the zone between and including the epicentral region and the area in question, while the second kind (infra-area models) presents velocities within the respective area. The locations of hypocenters considerably improved when the new models were used instead of the standard one for the Balkan region. The large-scale variation of average velocities obtained by inter-area modeling was found to be relatively small both in the crust and in the upper mantle. On the other hand, the magnitude and distribution of station corrections and the resulting intra-area velocities point to relatively pronounced lateral velocity variation within some of the studied regions. The obtained velocities in most cases do not differ significantly when compared to the values reported in other studies. The most important exceptions occur in the epicentral area (central part of the External Dinarides) where the P-wave velocity in the upper crust is much higher then elsewhere, while the velocity in the upper mantle is found to be lower than that determined by DSS experiments. There is also an indication of pronounced variation of the Poisson ratio in this area.