SEISMOTECTONICS OF THE NORTHWEST EXTERNAL DINARIDES

The region of the tectonic contact between the Alps and the Dinarides is studied comparing all the available geological, geophysical and seismological data. The peculiar crustal structures, in particular the difference in thickness of the Alps, Dinarides, and Pannonian basin can be correlated to the seismically active zones. The highest seismicity is related to the Adria microplate underthrusting the Southern Alps beneath the Friulian piedmont arc. This movement produces a composite lateral slip and an underthrust which is subparallel to the Dinarides along the Yugoslav coast. The seismicity in western Yugoslavia is more diffuse than in Friuli although it is possible to pick out three narrow parallel bands with dextral shear subparallel to the Periadriatic-Vardar fault system which separate the Apulia from the Pannonian area. The interaction of this system with the sinistral strike-slip faults of the western Carpathians belt enhances the seismicity of the easternmost sector of the Alps. Analogies and differences in the seismotectonic behaviour between central Friuli and western Yugoslavia are studied and a unique model with a vertical mechanical disengagement, at the rear of the compressive fronts of the Southern Alps and External Dinarides, is proposed. © 1990.