Seismotectonic and refraction seismic investigations in the border region between the Eastern Alps and the Pannonian Basin

Abstract

Focal solutions of four strong earthquakes and P signals of twenty-four smaller shocks of the active Mur-Mürz Valley, the Semmering Pass and the Vienna Basin. An ‘equivalent slip rate’ of 0.03 This feature agrees with the model of a subsiding Pannonian Basin. An ‘equivalent slip rate’ of 0.03 cm/year is roughly estimated from earthquake data 1903–1978. This rate does not include the creep rate, but it gives an idea of the magnitude of speed of geological processes in this area.

Refraction seismic data from the Alpine Longitudinal Profile 75 shows a low velocity zone in the upper crust of the seismic active East Alpine area but not in the aseismic part of the Pannonian Basin.

The eastern margin of the Eastern Alps and the Carpathians limits the Pannonian Basin, which has a special and interesting geological history. Many authors (Szadezky-Kardoss, 1966;Stegena, Ceszy andHorvàth, 1975) presented models of the genesis of the Pannonian Basin. They apply the concept of the ‘mantle diapirs’ to explain the following facts:

subsiding of the Pannonian Plate in comparison to the Alps, high terrestrial heat flow within the Pannonian Plate, decrease of the Moho depth from 40 km below the Eastern border of the Alps to 27 km below the Pannonian Basin. They claim that the Alpine-Carpathian interarc and basin represent the final stage of an orogenetic system where ‘subcrustal erosion’ leads to a thinning of the crust. Consequently the surface subsides and is covered by young sediments. They proved that this subsidence and sedimentation is more or less in isostatic equilibrium. The aim of this paper is to provide new arguments using focal solutions and refraction seismic investigations.