Landslides triggered factors analysed by time lapse electrical survey and multidimensional statistical approach T. Lebourg a, ⁎, M. Hernandez a , S. Zerathe a , S. El Bedoui b , H. Jomard c , B. Fresia a a UMR 6326, azur, CNRS-UNS-IRD-UPMC, 250 rue A. Einstein, 06560 Valbonne, France b LRPC Nancy — 71 rue de la Grande Haie, 54510 Tomblaine, France c Institute of Radioprotection and Nuclear Safety (IRNS), Fontenay-aux-Roses, France abstract article info Article history: Received 1 October 2009 Received in revised form 26 April 2010 Accepted 2 May 2010 Available online 10 May 2010 Keywords: Landslide Electrical resistivity tomography Time lapse survey Statistical analysis Triggering factors A temporal imagery of water circulation in a landslide by Electrical Resistivity Tomography (ERT) was conducted to identify spatially and temporally the coupling between rainfalls, consecutive water inflows in a sliding mass, and induced resistivity variations. This work is based on a multi-scale experimental approach applied on the “Vence” landslide (South-eastern France) which is characterised by a sandy-clay sliding mass on a marly limestone substratum mostly controlled by high rainfall events. At the landslide scale, historical, geological and geotechnical data combined with field investigations and the interpretation of three ERT allowed the definition of a geometrical model of the landslide and the calibration of the resistivity values. On the basis of these results, a permanent time lapse ERT survey was designed on a specific part of the landslide, coupled with water level acquisition (piezometric levels) and rain fall events. Results covering a three-month period are showed. The statistical analyses of all the physical parameters measured during the three months of investigation show that the matrix of correlations highlighted strong correlations between the rainfall, piezometric elevation and the resistivity. These first results show an accurate answer resistivity/piezometric elevation that can be associated as a precursor of the reactivation of the landslide. © 2010 Elsevier B.V. All rights reserved. 1. Introduction A better knowledge of landslide processes requires the character- isation of the triggering factors and their impact on landsliding. These factors are often time dependent and for this reason it is very complex to have a quantitative approach without a permanent in-situ investi- gation measurement. In most of the landslide processes, fluids are considered as one of the most important triggering and increasing factors. In order to better assess risks associated to a landslide, it appears important to localize and understand the fluid movements through the landslide. Since ten years, the use of non-destructive geophysical methods was developed to obtain some quantitative data about slope movements: slip geometry of the surfaces, faults networks and also water flows (Eberhart-Phillips et al., 1995; Lapenna et al., 2003; Rizzo et al., 2004; Friedel et al., 2006). Particularly sensitive to the water content and the slope structure, the electrical resistivity tomography is one of the most suitable approaches for the landslide study. This method is widely applied to obtain 2D or 3D high-resolution images of the resistivity variation in a geological system (Griffiths and Barker, 1993). During the last few years, a large number of electrical imaging has been conducted to acquire information about landslide structures (Robain et al, 1996; Lebourg et al., 1999; Lebourg and Frappa, 2001; Wise et al., 2003; Colella et al., 2004; Jomard et al., 2010). However, very few studies have been realized in order to obtain data on the water spatiotemporal distribution/variation and its role in landsliding. Recently, a first attempt has been successfully realised on the La Clapière landslide (Alps Maritimes, SE France) (Jongmans et al., 2000: Demanet et al., 2001; Lebourg et al., 2005; Jomard et al., 2006, 2010). Those results allowed the identification of the sliding surface and the network water flow paths, concluding in a strong influence of the draining capability of inherited tectonic structures. This study is based on an approach using electrical resistivity method, with a temporal follow-up, on a landslide located in Vence (Alps Maritimes, SE France, Fig. 1). The aim of this work is to characterize the evolution in both space and time of the natural resistivity variations in the drainage channel system. The choice of this landslide was motivated by the size of the landslide that is well adapted to such dense geophysics researches, but also the geological and hydrogeological frameworks with a sub- stratum structure (fractured calcareous) and groundwater transfer Engineering Geology 114 (2010) 238–250 ⁎ Corresponding author. Tel.: +33 4 9294 2670; fax: +33 4 9294 2610. E-mail address: lebourg@geoazur.unice.fr (T. Lebourg). 0013-7952/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2010.05.001 Contents lists available at ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo