The Application of ERT for the Geometrical Analysis of the Sebrango Landslide, (Cantabrian Range, Spain)

Electrical resistivity tomography (ERT) was applied to the geometrical characterization of the Sebrango Landslide reactivation (Cantabrian Range, Spain), which threatened the villages of Sebrango and Los Llanos on June 2013. The Sebrango Landslide is a 1.2 km-long landslide that episodically affects a hillslope located at the northern margin of the Deva River, at the northern sector of the Liebana Syncline. ERT surveying offered the opportunity to investigate the unexposed geometry of the landslide just after finishing the 2013 paroxysmal stage, while other surveying techniques, as core logging, were ruled out for safety and local government regulation during the hazard emergency. The obtained resistivity images provided information on the thickness of the terrain involved by the landslide, on the location of the inner rupture surfaces, and on the groundwater flow pattern within the hillslope. The results suggest that the landslide involves a 40–60 m-thick mass of complex structure. The resistivity images show a profuse groundwater flow within the slid mass, especially in the header area affected by the 2013 reactivation. The images also show a preferential groundwater flow longitudinally to the axis of a secondary landslide lobe, at the eastern sector of the landslide body, pointing to this sector is that actually shows greater deformation, as opposed to the main lobe oriented NW-SE. The landslide geophysical model was constrained by a core logging and monitoring campaign conducted during the subsequent months. From a geomorphological perspective, our results suggest that the particular entrenchment dynamics of the Deva River is playing a key role as a preparatory landslide factor.