A Model of Composite Seismic Sources for the Lower Rhine Graben, Northwest Europe

Abstract

Abstract The Lower Rhine Graben (LRG) straddling the border zone of Belgium, the Netherlands, and Germany, is an active tectonic structure in continental northwest Europe. It is characterized by northwest–southeast oriented normal faults, and moderate but rather continuous seismic activity. Many faults have been mapped in the LRG, but so far a model of fault hierarchy or fault segmentation has been lacking. In the frame of a European database of seismogenic sources, we have devised a seismic‐source model for the LRG consisting of so‐called composite seismic sources. Each composite seismic source may encompass one or more segments, but it is unlikely that a segment would extend across more than one source. We distinguish 15 seismic sources based on major stepovers, bifurcations, gaps, and important changes in strike, dip direction, or slip rate. The sources are partitioned into one or more informal fault sections, each with an associated surface trace. For each source, we describe the limits and the composing fault sections, and present the geological arguments for their existence. We have compiled all relevant data concerning the seismic‐source parameters required for the database, putting lower and upper bounds on strike, dip, rake, slip rate, and depth, and an upper bound on earthquake magnitude. This source model should provide a new basis for modeling seismic hazard, as well as for guiding further paleoseismic studies in the LRG. Online Material: Detailed maps of the composite sources in the Lower Rhine Graben, 3D views of the fault model, and a table with parameters of earthquake focal mechanisms and detailed information sheets for each composite seismic source.