Abstract The Lower Rhine Graben (Central Europe) is a prime example of a seismically active low-strain rift zone characterized by pronounced anthropogenic and climatic overprint of structures, and long recurrence intervals of large earthquakes. These factors render the identification of active faults and surface ruptures difficult. We investigated two fault scarps in the Lower Rhine Graben, to decipher their structural character, offset and potential seismogenic origin. Both scarps were modified by anthropogenic activity. The Hemmerich site lies c. 20 km SW of Cologne, along the Erft Fault. The Untermaubach site lies SW of Düren, where the Schafberg Fault projects into the Rur River valley. At the Hemmerich site, geomorphic and geophysical data, as well as exploratory coring reveal evidence of repeated normal faulting. Geophysical analysis and palaeoseismological excavation at the Untermaubach site reveal a complex fault zone in Holocene gravels characterized by subtle gravel deformation. Differentiation of tectonic and fluvial features was only possible with trenching, because fault structures and grain sizes of the sediments were below the resolution of the geophysical data. Despite these issues, our investigation demonstrates that valuable insight into past earthquakes and seismogenic deformation in a low-strain environment can be revealed using a multidisciplinary approach.

We provide a synthesis of the long-term earthquake activity in the region of northwest Europe between the Lower Rhine Embayment and the southern North Sea. Reevaluated historical earthquake and present-day seismological data indicate that much of the known seismic activity is concentrated in the Roer graben. Nevertheless, the three strongest known earthquakes with estimated magnitude ≥ 6.0 occurred outside of this active structure, in the northern Ardenne, the southern North Sea, and the Strait of Dover. During the past 700 yr, destructive earthquakes generally have occurred at different locations, indicating a migration of seismicity with time. Because in plate interiors the present seismic activity does not necessarily reflect past and future activity, we discuss the necessity to use the geologic record to infer long-term earthquake activity. Thus, we synthesize and discuss paleoseismic investigations in the Roer graben that provide evidence that large earthquakes with magnitude up to 7.0 have occurred since the late Pleistocene. We also show that tectonic deformation is close to or below the accuracy of current geodetic techniques. Thus, it is necessary to have longer periods of observation to compare present geodetic deformation rates with the observed seismic moment release and the geologic strain rates. Based on these results, we present methods to define seismic zoning and evaluate the maximum credible earthquake and its magnitude relevant for seismic hazard assessment.