INTEGRATED GEOLOGICAL MAPPING IN THE BORDER REGION BETWEEN GERMANY AND DENMARK BASED ON GEOPHYSICAL TECHNIQUES

Geophysical techniques are increasingly used worldwide as tools for hydrogeological mapping and often they are requested in order to perform proper groundwater management. Buried valleys, faults, layer boundaries, different sedimentary units and glaciotectonic structures constitute geological elements that are vital to identify and outline in 3D models if used for such purposes. In a study area covering 730 km² across the border between Germany and Denmark a combination of an airborne transient electromagnetic survey (performed with the SkyTEM system) and a high-resolution seismic survey has proven very useful for an integrated mapping of geological elements like the above-mentioned. The spacing between flight lines is 200-250 m giving a total of about 3200 line km. About 38 km of seismic lines have been collected. Faults bordering a graben structure, deep and shallow buried tunnel valleys, glaciotectonic thrust structures, marine clay units and interglacial deposits are all examples of geological elements that have been identified and delineated in the geophysical data. Some of the faults and other subsurface structures are additionally detected on LIDAR data. Although the westernmost part of the study area along the North Sea coast is saturated with residual saltwater and the TEM data therefore is severely influenced by the increased electrical conductivity here, buried valleys and other features are still revealed. The data also provide an excellent picture of the groundwater salinity distribution in the area and gives important information on the fresh-saltwater boundary.