CRUSTAL-SCALE STRUCTURE OF THE SOUTHERN RHINEGRABEN FROM ECORS-DEKORP SEISMIC-REFLECTION DATA

Two seismic lines with a total length of 207 km were shot in 1988 by the French and German deep reflection seismic groups (ECORS and DEKORP) across the Rhinegraben. The southern profile shows the following characteristics. (1) The Moho discontinuity is marked by a strong reflector, except beneath the eastern part of the graben and at the western end of the profile. Its depth is only 8 s (two-way traveltime) below the graben and increases progressively to 10 s below the Lorraine basin. (2) The layered lower crust reveals strong variations in the seismic signature and apparent thickness. (3) East-dipping reflectors in the middle crust may be attributed to Variscan features. (4) The Lorraine basin is characterized by Carboniferous and Permian-Triassic strata onlapping the Vosges crystalline basement. (5) The Rhinegraben is markedly asymmetric, possibly owing to extensional movement along a listric shear zone, which appears to merge at depth with a flat-lying detachment in the ductile lower crust. The Oligocene sedimentary infill was controlled by an east-dipping normal fault whose vertical throw is about 3 km.