On the origin of late Quaternary palaeolandslides in the Li�ge (E Belgium) area

Abstract

A series of palaeolandslides is described in eastern Belgium, with geophysical investigations, trench analysis and a number of 14 C dates complementing the field description. The proposed sliding mechanism stresses the importance of initial liquefaction of the upper Cretaceous Aachen sands underlying the~30-m-thick Vaals Clay Formation, in which all landslides are developed. Slope-stability analyses support the hypothesis of sudden landsliding and yield further useful information to discuss their origin. A main difficulty in determining the landslide trigger arises from insufficient absolute dates. Assuming that all landslides occurred simultaneously, we weigh the probabilities, respectively, of a climatic and a seismic trigger. Although the 150 a.d. possible date of landslide initiation falls close to one of the wettest periods of the Holocene, the spatial distribution of the deep slides and their proposed mechanism strongly suggest a seismic origin in connection with a rupture of the nearby Ostend segment of the active Hockai fault zone. However, considering that the nearby 1692, Verviers earthquake apparently caused no ground failure, it is probable that both the climatic and seismic triggers were jointly needed to provoke such deep and extended landsliding on moderate, generally stable slopes.

Mapping landslide susceptibility from small datasets: A case study in the Pays de Herve (E Belgium)

“…Though highly probable, the seismic origin of the pre-existing landslides, and thus the role of active faults as triggering factor, cannot be definitely proved (Demoulin et al, 2003). Moreover, one may wonder whether, beyond the need for the combined occurrence of the Aachen sands and the Vaals clays, the presence of an overlying chalk cover had any influence on the spatial distribution of the landslides.…”

“…Meaning of the "proximity of Gulpen outcrops" and "proximity to active fault" parameters and choice of the final prediction map At first glance, the spatial distribution of the landslides of the Pays de Herve might seem to be partly dependent on the absence of an overlying chalk cover. However, a closer look at this distribution only revealed a weak relationship, which could not be clearly explained (Demoulin et al, 2003). To cover this uncertainty, we ran two types of models with different lithological map units.…”

“…Several ancient large landslides have recently been described to the east of Liège, in eastern Belgium (Demoulin et al, 2003) (Figs. 1 and 2).…”

“…Demoulin et al (2003) showed that landsliding was initiated by earthquake-triggered liquefaction of some layers in the Aachen sands, which first induced the translational gliding of the lower part of the slope, which in turn caused retrogressive rotational sliding in the upper part of the slope. The combined presence of the Aachen sands and the overlying Vaals clays was thus necessary for these landslides to occur.…”

“…Detailed investigation carried out by Demoulin et al (2003) showed that they were most certainly triggered by an earthquake on the NNW-striking Ostende segment of the Hockai fault zone (Fig. 1).…”