Geoelectrical tomographies for the study of some landslide areas in the Lucanian Apennine chain (southern Italy)

In the frame of the two projects supported by the Italian Ministry of Research: "Design of geophysical monitoring network in areas of the Basilicata Region characterized by a high hydrogeological hazard" and "Geomorphological study and landslides control in some areas of the Basilicata region characterized by historical-cultural heritage", we developed a research activity focussed on a 2D electromagnetic monitoring and modelling of landslide bodies. Basilicata region (Southern Italy), being dissected by numerous and often significant rivers and characterized by the outcrop of terrains with bad mechanical properties, is one of the more exposed regions of the southern Apennine chain to hydrogeologic hazard and shows a complete panorama of mass movements. In order to study some landslide areas located in the Basilicata region, such as Varco Izzo, Latronico, Campomaggiore and Maratea, we carried out 2D electrical resistivity imaging (ERI), 2D-3D self-potential tomographies and maps, combining advanced technologies for data acquisition and new methods for data inversion (Loke and Barker, 1996; McCann and Forster, 1990; Patella, 1997). The geophysical results allowed us: to outline the discontinuity between landslide material and bedrock, to identify the possible reactivation surfaces, to obtain useful information about the thickness of the mobilised material and the main patterns of the underground fluid flow. Geophysical results were compared with the data coming from geological and hydrogeological surveys and from the analysis of aerial photo and boreholes. The good correlation between the main anomalous geoelectrical zones, the main structural lineaments and hydrogeological characteristics of the investigated areas, allowed us to consider the used geoelectrical methods as a possible powerful tool to investigate landslide areas characterised by very complex geology. The surface velocity obtained by GPS, however, could be not really representative of the deep movements of gravitational phenomena. This means that in the monitoring of landslides it’s not possible to leave out of consideration the information coming from other techniques of investigation. In the paper are summarised the geological and geomorphological studies and the main results of the monitoring survey carried out on some areas located in Basilicata region (southern Italy). The landslide monitoring system is made up by traditional survey system and new technologies. One test site was at Lauria locality, an urbanized area interested by large and active landslides; the lasts are subject to frequent reactivations causing severe damage to the urban structures. The results of GPS survey, in good agreement with the results of the geomorphologic study, show that some of the analysed landslides are subject to a slow, continue deformations. Other results come from the survey (in progress) about slope instability processes observed in two different areas of the "Parco Archeologico Storico Naturale delle Chiese Rupestri del Materano" where fine rupestrian heritages are present. In these areas, the considerable acclivity of the slopes and the lithological defects and intense fracturing state of carbonate rocks cause rapid mass movements of the blocks (rock falls, topples and rockslides). On the basis of geological and geomorphological studies, the potentially unstable carbonate blocks that need survey have been defined. The design of the survey system is made up by a traditional topographic survey, GPS measures and a deformation measurement system.