Geophysical reconnaissance of the Pays de Herve landslides, Belgium: case study of three active paleo-slides in a dissected tableland

Abstract The Pays de Herve region in East Belgium is characterised by widespread slope instability. Some of these Quaternary paleo-landslides are still active, showing subsidence phenomena that can be related to the presence of weak subsurface materials such as clays (locally topped by weathered chalk) overlying a discontinuous sand-silt layer. This study provides a detailed characterisation of three active landslides in the area, with a particular focus on the Manaihan landslide, which is the most active and has also caused damage to surrounding buildings. To investigate these landslides, an integrated geophysical approach was applied, combining electrical resistivity tomography, P-wave seismic refraction, multichannel analysis of surface waves, and microseismic ambient noise measurements (H/V analysis). Each method has intrinsic limitations, but their combined use allowed for a comprehensive analysis of the sliding surfaces. While the first three techniques provided detailed information on limited sectors of each landslide, the ambient noise measurements enabled the coverage of the entire landslide areas. This integrated approach, combining microseismic ambient noise frequency analysis, allowed for a detailed mapping of the Manaihan landslide’s subsurface and the creation of a 3D geological model of the site. The results align well with the geophysical imagery collected, allowing the precise identification of the landslide bases and enhancing the understanding of the subsurface structure in the Pays de Herve region.