Geophysical investigations of groundwater relevant subsurface structures in Northern Germany

Beside the salt domes the subsurface structure in Northem Germany and adjacent countries is characterized by a system of glacial channels and valleys that are cut into Tertiary sediments down to a depth of more than 500 m (Fig. 1). They are filled with Quatemary sediments and are not visible from the surface. This kind of subsurface structure is highly important for the hydrogeological conditions. The glacial valleys can be filled with sandy material and thus be a good groundwater reservoir or conneet upper and deeper aquifers (Fig. 2, left) or they can be filled with low permeable clay bearing moraine material and so interrupt or disconneet the aquifers (Fig. 2, right). Normally a mixture of both extreme positions can be found, also a valley can show lateral changes in the hydrogeological characterization.