CRUSTAL STRUCTURE OF SOUTHERN GERMANY FROM SEISMIC REFRACTION DATA

Seismic refraction data obtained along fifteen lines in southern Germany in the 60's and in 1982-1984 were used to derive a 3-D model of crustal structure below the "South-German Triangle" bounded by the Bohemian Massif in the east, the Alps in the south and the Rhinegraben in the west. Both the older and the more recent data were interpreted with the same techniques taking into account the results of published crustal information. Along three lines the observations could be interpreted as a reversed system and here both traveltime and amplitude information was used applying two-dimensional (2-D) raytrace modelling resulting in 2-D models controlled by traveltimes and amplitudes. These three crustal cross sections supplement an existing 3-D model for southwest Germany. The characteristic features of the crustal structure of the South-German Triangle can be summarized as follows:. An intermediate boundary, identified by many authors as Conrad discontinuity, is found in its central part at depths between 16 and 18 km. Towards the northwest and south it descends to 20 and 22 km, respectively. In the region of the Black Forest it occurs at a rather shallow level at depths of only 14 km. The depth to the Moho reaches values between 27 and 28 km in the central part of the South-German Triangle. Beneath the Black Forest and the southwestern part of the Swabian Jura, the crustal thickness is reduced ranging from 25 to 26 km. To the northwest the Moho dips only slightly, but to the northeast under the Bohemian Massif it reaches depths up to 35 km. Beneath the northern foreland of the Alps the Moho descends gradually to about 40 km depth near the northern margin of the Alps. A low-velocity zone in the middle crust changes its characteristics throughout the area of investigation and is even absent in some areas. The velocity decrease is generally less than 0.3 km/s, except under the central and northern Black Forest, where the velocity decreases by as much as 0.5 km/s. The existence of a laminated lower crust, i.e. a crust which comprises layers of alternating high and low velocity as was found beneath the Black Forest, is also indicated in some of the data obtained in 1982-1984 and shown in this contribution. © 1990.