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In order to investigate an often-quoted coincidence of an intracrustal velocity jump (the Conrad discontinuity) and lower crustal reflections (found in tectonothermally young areas), 54 reflection seismic profiles have been analysed and combined with 50 refraction seismic profiles adjacent to the reflection lines.

Variable parameters of the continental crust are: crustal age, heat flow, reflectivity, thickness and velocity. While heat flow and reflectivity decrease, crustal thickness increases with age. For stable crustal regions we present a correlation between crustal thickness and mean crustal velocity. The evaluation is based on more than 270 data points. It is shown that mean crustal velocity is higher in thicker crusts. An attempt is made to relate this observation to crustal growth by accretion from below.

Within the DEKORP project (DEKORP: Deutsches Kontinentales Reflexionsseismisches Programm) a joint deep seismic reflection venture with the BELCORP (Belgian Continental Reflection Seismic Programme) group of the Belgian Geological Survey was carried out in 1987 across the Rhenish Massif, a part of the mid-European Variscides. This orogenic belt developed in the Upper Devonian/Carboniferous. Mostly Devonian rocks crop out at the surface. The Rhenish Massif is bordered by two sedimentary troughs: the sub-Variscan Foredeep in the north and the Permo-Carboniferous Saar-Nahe Basin in the south. In the east-west direction it is subdivided by the axial depression of the Eifel Nord-Süd Zone. The aim of the survey which totals almost 220 km of seismic profiling, was to investigate the crustal structure of the western part of the Rhenish Massif and to compare it with the line DEKORP 2-N which crosses the eastern portion of the massif. The results indicate the presence of NW-vergent tectonics of various styles that can often be traced down to deep parts of the crust. Horizontal Variscan compression plays a dominant role in the northern part while post-Variscan extension seems to dominate in the Saar-Nahe Basin, although even there traces of Variscan compression seem to be preserved in the middle crust. Common characteristics of the pre-Palaeozoic basement, differences between the western and eastern parts of the Rhenish Massif, and the deep extension of the Aachen Thrust (Faille du Midi) have been clearly observed. This prominent thrust in the north with its characteristic ramp and flat structure has been followed over 100 km length down to 15 km depth. It contrasts sharply with the very complex deep fault system in the south, separating the post-orogenic Saar-Nahe Basin from the Hunsrück mountains. The integration of accompanying geophysical and geological studies provides a new synoptic picture of the evolution and tectonics of this key area of Central Europe.