2. Paleoseismological studies

2.1. The Feldbiss Fault in Belgium

2.1.1. Introduction

The dominant tectonic structure in north-eastern Belgium is the Neeroeteren Fault, which separates the Campine Plateau to the SW from the Bocholt Plain (part of the Roer Valley Graben) to the NE. Its connection with the Feldbiss Fault in the SE Netherlands and Germany was established by geoelectric measurements in the intervening alluvial plain of the Meuse river (Paulissen et al., 1985). The tectonic activity of the fault is mainly attested at depth by seismic reflection profiles (Fig. 2) showing more than 500 m offset of Neogene deposits (Demyttenaere and Laga, 1988). North of the city of Bree, the Feldbiss Fault is split up into three branches, (from W to E) the Grote Brogel Fault, the Reppel Fault, and the Bocholt Fault, among which the total offset is more or less equally divided.

Fig. 2 -  Seismic reflection profile (courtesy of the Belgian Geological Survey) across the Feldbiss Fault in Opitter. Stratigraphy slightly modified from Demyttenaere & Laga (1988).

The Belgian portion of the Feldbiss Fault appears to be seismically quiet, however: the largest event recorded this century was a M 3.7 shock near Stramproy in 1960; historical earthquakes are equally undocumented in northeastern Limburg, although important events are known to have occurred along the German part of the fault (see Fig. 1 and Table 1).