Relevance of active faulting and seismicity studies to assessments of long-term earthquake activity and maximum magnitude in intraplate Northwest Europe, between the Lower Rhine Embayment and the North Sea

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 > or =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.