The European Geotraverse seismic refraction experiment of 1986 from Genova, Italy, to Kiel, Germany

Abstract

For the first time a continuous coverage with modern seismic refraction data has been achieved on a line from North Germany to North Italy. From this data we derived a detailed crustal model which ties together most of the scattered earlier data. A tectonic cross section can be constructed which includes the Caledonides and the Variscides of Germany as well as the young Alpine orogene of Switzerland and North Italy. As part of the European Geotraverse (EGT) a seismic refraction experiment was carried out in September 1986 with shots along a 1200 km line between Genova (Italy) and Kiel (F.R.G.) and with fan profiles for the P g and P MP phases in the Po Plain and the northern Apennines. This paper describes the fieldwork and presents a first interpretation of some of the data recorded between the Southern Alps and the North German Lowlands. For the area north of the Alps a preliminary two-dimensional velocity-depth model was derived. North of the Alps, under the Swabian Jura the crust-mantle boundary lies at a depth of about 26 km. Farther to the north the crust has a nearly constant thickness of 28 km. A characteristic feature of the velocity-depth model north of the Alps is the existence of a low-velocity zone in the middle crust. This zone seems to extend southwards underneath the Alps and it evidently vanishes under the North German Lowlands. In southern Germany the velocity decreases from 6.2 to 5.5 km/s below depths varying between 8 and 11 km. The thickness of this low-velocity zone varies between 3 and 5 km. In the same area a discontinuity with a velocity increase from 6.2 to 6.8 km/s rises from 20 km depth under the Alpine foreland to 17 km depth under the Rhön in the north and merges with the lower boundary of the low-velocity zone under the Rhön. Under the Variscan mountain area north of the Main river the low-velocity zone deepens, becomes thicker (depth range 10 to 17 km) and more pronounced. The lower crust between the northern Alpine foreland and the North German Lowlands is characterized by a velocity of about 6.9 km/s.