Paleoseismic investigations in the Lower Rhine Graben (LRG): Challenges and insights from a densely populated, tectonically active intraplate region

Assessing seismic hazard in tectonically active intraplate regions with slow slip rates (<0.1 mm/yr) is particularly challenging, especially when such regions are densely populated and extensively anthropogenically modified. Fault activity often remains undetected due to long recurrence intervals, limited surface expressions, and widespread anthropogenic overprinting. The Lower Rhine Graben (LRG), part of the European Cenozoic Rift System, exemplifies these conditions. In addition to its current low to moderate seismicity, the LRG region has experienced damaging historical earthquakes (e.g., Düren 1756, M_L 6.4; Roermond 1992, M_L 5.9), underscoring its seismic potential.

In this context, we conducted five paleoseismic investigations within the LRG to access direct geological records of past surface-rupturing events and fault kinematics. We focused on its most seismically active and structurally segmented subregions: the Roer Valley Graben and the Erft Block. The investigated fault segments include the Feldbiss Fault, Sandgewand Fault, Birkesdorfer Fault, Rurrand Fault, and the Louise Sprung.

All sites provide evidence of Late Pleistocene to Holocene surface-rupturing events, with single-event displacements of up to 70 cm and estimated magnitudes up to M 6.3. The faults are characterized by steeply dipping planes (70 – 80°), pure dip-slip kinematics, low slip rates (< 0.03 mm/yr), and show indications of hydraulic activity. At the Rurrand Fault and Louise Sprung, we observed induced aseismic creep linked to groundwater extraction, highlighting the need to distinguish natural from anthropogenic deformation.

Our results demonstrate the seismic potential of these faults and underline the importance of integrating paleoseismic data into regional seismic hazard assessments.