A seismic velocity model for the SW Baltic Sea derived from BASIN'96 refraction seismic data

Within the BASIN'96 project (Basin Analysis and Seismic Investigation in North Germany 1996) a marine survey gathered seismic data in the southwest Baltic Sea to study the Caledonian collisional zone between Baltica to the north and Alvalonia to the south. Additionally, the airgun pulses have been observed by several land stations. Special attention was paid to record good quality data on Rugen island aiming at linking offshore and land-seismic wide-angle observations. Therefore, a complex geophone array (the 'Star of Rugen') was designed to enhance the signal quality. The Star of Rugen data and other onshore observations in NE Germany and on Bornholm, an island in the Baltic Sea, have been used for P-wave velocity modelling. Important structures of the transition zone from Palaeozoic western Europe to the Precambrian Baltic Shield are imaged in the resulting three-dimensional velocity model. A pronounced basement high north of Rugen island indicates the location of the Caledonian Deformation Front (CDF). Velocities also reflect other prominent features, such as the Ronne Graben, a pull-apart structure of the Tornquist Zone, and the basement outcrops around Bornholm island. In the investigated area the Moho depth varies between 27 and 33 km. A high-velocity layer in the lower crust below the NE German mainland may indicate genetic relations to Baltica. The structural continuity, however, is disturbed by a velocity decrease in an area north of the CDF. Sporadic, but strong reflections from the upper mantle below the CDF seem to be consistent with the reflection seismic data [DEKORP-BASIN Research Group, 1999. Geology 27(1), 55-58]. (C) 1999 Elsevier Science B.V. All rights reserved.