Seismotectonic activity in East Belgium: relevance of a major scarp and two associated landslides in the region of Malmedy

Geomorphological markers such as scarps, river diversions and slope failures can be used as proxy indicators for the seismotectonic activity of a region. This study concentrates on the Malmedy-Bévercé area, E-Belgium, where formerly unknown geomorphological features have been recently discovered in the frame of a new regional geological mapping campaign. The area is characterised by gentle to locally very steep slopes along the Warche valley crossing the Stavelot Massif and the Malmedy Graben. Coupled with a LiDAR-DEM and UAV imagery analysis, field mapping has revealed a steep scarp extending near two landslides on the southern hillslopes of the Warche valley at Bévercé. These slope failures developed in the Permian conglomerates of the Malmedy Formation (also known as the Poudingue de Malmedy), which represent the infill of the Malmedy Graben. Roughly perpendicular to the graben axis, the scarp has a N330°E orientation similar to that of the seismotectonically active Hockai Fault Zone that crosses the Malmedy region in this area. In this paper, we present the geological and geomorphological context of the Bévercé scarp and of the
largest landslide. Furthermore, we demonstrate the results of a geophysical reconnaissance survey of the structures (seismic refraction and electrical resistivity profiling). The geophysical results highlight a vertical displacement of the seismic layers and laterally changing electrical properties across the scarp, with very low resistivity values in its middle part. A low resistivity zone in the subsurface can also be found within the larger landslide, right in the prolongation of the scarp. All these observations hint at the presence of a major, probably seismically active, fault belonging to the eastern border of the Hockai Fault Zone.