Prediction of the Process of a Slowly Moving Loess Landslide by Electrical Resistivity Tomography

A slowly moving loess landslide along the River Danube in South Hungary was studied using electrical resistivity tomography (ERT). The aim of the research was to determine the fracture system of the study site. It seems to be the only possibility to get information about the landslide and its further evolution due to the homogeneous composition of the loess. The mass movement was expected to occur in the direction of the identified crack openings. The applicability of the ERT technique for such a supposedly dense fracture system was studied by numerical modelling and the results have been verified in the field. It was shown that it is especially important to carry out the field measurements following dry periods; otherwise the interpretation may become extremely difficult if not impossible. The dip of the fractures could not be observed and they could not be explored deeply. It was possible to map their surface projection to get the desired information about the structure of the landslide. Fracture zones could be especially well localized enabling the prediction of the positions of future rupture surfaces and thus also the delineation of the endangered zone. Although the area outside of the one that already subsided is not endangered yet, the area which has already started to move is going to break into two. Parts of the about 5 m wide blocks at the front of the landslide may fall or slide down anytime. The area below the buildings was assumed to move as one unit. Most of our predictions have been verified by the mass movements which occurred about one and half years after the measurements. The ERT method proved to be a good tool to characterize the fracture system of such a landslide area, enabling the prediction of future rupture surfaces and also delineation of the endangered area. Its use is therefore highly recommended to monitor landslides.