Recent crustal movements in the southern Black Forest (western Germany)

Abstract

Precise levelling data are examined in the southern Black Forest massif by comparing them analytically along levelling profiles. Instead of generalizing regional vertical motion trends, the method emphasizes the current activity of accurately located individual structural elements. Measured recent crustal movement rates range from 0.2 to 1.1 mm/year for the 1930–1961 (1972) period, the inferred motions corresponding to aseismic fault creep. Based on the near infrared band image of a Landsat MSS scene, a lineament map of the study area is compared with the recent crustal movement (RCM) map. The Upper Rhine graben eastern border fault between Badenweiler and Freiburg displays the highest RCM: these displacements are consistent with the geological motion and the topographic expression of that structure. Within the massif, both the lineament map and the RCM map demonstrate the predominant role played by WNW/ESE- to NW/SE-striking structures in accommodating the deformation. Moreover, with the seismic dislocations in the southern Black Forest taking place also mainly on N120 and N20 faults, it is most probable that these active structures are deep-reaching zones of crustal weakness. To some extent, seismicity and RCM appear, however, to be mutually exclusive in their spatial distribution, the seismic Black Forest flexure and Dinkelberg block being opposed to the aseismically moving eastern and northern parts of the study area.