Erdbeben und tektonik in Südwest-Deutschland

Abstract

The earthquakes in southwestern Germany are concentrated in three different regions: 1. (1) The eastern earthquake region (Lake of Constance, Molasse Basin, the central and western Swabian Jura and the Fildergraben near Stuttgart). 2. (2) The southern and central Black Forest. 3. (3) The Upper Rhine Graben. Most earthquakes take place along variscan or prevariscan strike-slip faults (e.g., all earthquakes in the Swabian Jura since 1911; in the Rhine Graben the earthquake of 1933 near the city of Rastatt). Dip-slip earthquakes could be found in the western part of the Lake of Constance, in the Black Forest and in the Rhine Graben (e.g., the shock serie near the city of Karlsruhe in 1948). The seismic events north of the Lake of Constance (Oberschwaben, 1935 and 1965) are caused by motions on transcurrent fault planes slightly tilted against the earth's surface. There exists an energy maximum for depths between h = 2 km and h = 10 km, another less important maximum was determined at the depth of h = 15–20 km. The latter focal depths have been observed frequently in the Black Forest, more seldom in the environment of the Lake of Constance. Therefore the Black Forest forms a seismic “deep-focus” zone between the Rhine Graben and the eastern part of southwestern Germany. The distribution of principal tectonic stresses, as deduced from first motion studies, shows a very close relation between the Alps and their northern foreland. In both regions a southeast-northwest direction of principal pressure is dominating. The wandering of aftershocks inside an earthquake region can be explained by motions along secondary faults, resulting from the variation of the stress field in the neighbourhood of the main fault. It seems probable that the earthquake activity in the Alps and in the Rhine Graben region results from the actual orogenetic activity in the northern Apennine mountain range.