In order to better constrain the observations achieved on the site, several electrical tomography surveys were carried out on the landslide area. The electrical tomography principle fits well to the description of landslides and to the study of hydraulic subsurface circulations. More precisely this approach does not enable to locate accurately interfaces and formations but define the geometry and power with a metric resolution.
A first electrical tomography survey (4 profiles dipole-dipole and pole-dipole), performed by the research laboratory Geoazur, allowed to put forward a structural variation corresponding to the landslide area between 10 to 15 m depth, which matches the results of the inclinometry study.
Profiles performed at the first electrical tomography survey
The inverted data show an upper bed characterized by low resistivities corresponding to clay sands and a lower bed more resistant corresponding to the underlying limestone. Moreover the study reveals the existence of fault zones at the bottom of the landslide that are pointed out by low resistivity strips in the resistant limestone bed, homogeneous in the other profiles.
A second survey, coupled to field mapping, thus was conducted in order to confirm the previous results (powers and interfaces of formations) and to constrain faults in depth, not well defined during the first survey. We used the dipole-dipole (dd), pole-dipole (pd) and pole-pole (pp) methods for each of the profiles. The advantage to work with the three methods is to be able to change the depth scale during the data processing despite the loss of accuracy on the pp and pd profiles.
The profiles give the following informations and interpolations: