A possible surface rupture of the 1756 Düren earthquake (Lower Rhine Graben)

Strong and rare or infrequent intraplate quakes in densely populated areas pose a significant risk to humans, infrastructure, and the environment. The Lower Rhine Graben is tectonically one of the most active zones in central Europe, and it is part of the European Cenozoic rift system. The destructive 1756 CE Düren Earthquake (Mw 6.4±0.3; located in western Germany), or the  1992 CE Roermond Earthquake (Mw 5.9; located in eastern Netherlands), both caused by normal faults of the Lower Rhine Graben, inflicted tremendous damage and demonstrate the need of hazard assessments and prevention in this highly industrialized area. Therefore, mapping and detecting of the traces, historical activity and kinematics of faults and related fault systems, is of high importance for hazard assessment of critical infrastructure   (i.e. pipelines, highways, lifelines) and cities in the Dutch, Belgian and German border region.

The 1756 CE Düren earthquake was one of the most destructive ones in the area, and in entire Central Europe, the observed damage (landslides, sackungen) and magnitude suggest a surface rupturing event. The causative fault is still under debate, also epicentral area and hypocentral depth remain enigmatic although different studies investaged several faults in the area, e.g. the normal Rurrand Fault or the Schafberg Fault. The Rurrand Fault does not exhibit seismic surface rupturing events younger than 2.3 ka, whereas the Schafberg Fault is much too short to produce a M > 6 event and trenching failed.

Trenching at the Birkesdorfer Sprung (or Fault), a NW-SE trending normal fault with a minimum length of c. 9 km, revealed a set of SW dipping normal faults associated with colluvial wedges and unconformities. Geophysical ground survey methods (GPR and ERT) as well as GIS-based morphotectonic analyses identified a long fault trace. Radiocarbon (¹⁴C) charcoal dating of displaced colluvial deposits revealed very young ages of c. 240 y BP and evidence for a second event older than c. 3.6 ky BP, the latter has been already described. However, this older event can be bracketed here much better in between 9.1 ± 1.5 ky BP and 3.6 ± 0.03 ky BP. Hence, in the Holocene, the recurrence period of surface rupturing earthquakes is lower than thought before and other seismic sources, such as the Birkesdorfer Fault must be considered.