Potential of Electrical Resistivity Tomography to Detect Fault Zones in Limestone and Argillaceous Formations in the Experimental Platform of Tournemire, France

Abstract

International audienceThe Experimental platform of Tournemire (Aveyron, France) developed by IRSN (French Institute for Radiological Protection and Nuclear Safety) is located in a tunnel excavated in a clay-rock formation interbedded between two limestone formations. A well-identified regional fault crosscuts this subhorizontal sedimentary succession, and a subvertical secondary fault zone is intercepted in the clay-rock by drifts and boreholes in the tunnel at a depth of about 250 m. A 2D electrical resistivity survey was carried out along a 2.5 km baseline, and a takeout of 40 m was used to assess the potential of this method to detect faults from the ground surface. In the 300 m-thick zone investigated by the survey, electrical resistivity images reveal several subvertical low-resistivity discontinuities. One of these discontinuities corresponds to the position of the Cernon fault, a major regional fault. One of the subvertical conductive discontinuities crossing the upper limestone formation is consistent with the prolongation towards the ground surface of the secondary fault zone identified in the clay-rock formation from the tunnel. Moreover, this secondary fault zone corresponds to the upward prolongation of a subvertical fault identified in the lower limestone using a 3D high-resolution seismic reflection survey. This type of large-scale electrical resistivity survey is therefore a useful tool for identifying faults in superficial layers from the ground surface and is complementary to 3D seismic reflection surveys

Evolution stages of large deep-seated landslides at the front of a subalpine meridional chain (Maritime-Alps, France)

“…ERT has been widely applied to these types of problems and many recent studies have shown its usefulness in defining geological structure, fault geometry, landslide boundaries (sliding surfaces), and deep water circulations (Naudet et al, 2008;Fazzito et al, 2009;Heincke et al, 2010;Jomard et al, 2010;Lebourg et al, 2010;Pánek et al, in press). In this study, ERT was useful because of 1) the relatively simple geological structure of the La Marbrière slope (monoclinal layers and vertical faults) that would result in simple inverted models, and 2) high resistivity contrast between limestone and mudstone or a fault zone and limestone that facilitate identification of stratigraphic boundaries to evaluate fault offsets (Caputo et al, 2003;Nguyen et al, 2007;Adepelumi et al, 2008;Schrott and Sass, 2008;Gelis et al, 2010).…”

Investigations of a Cretaceous limestone with spectral induced polarization and scanning electron microscopy

“…For example, Jurassic limestones and dolomites deposited in a Mesozoic marine basin in France were investigated by Gélis et al (2010), while Cavinato et al (2006) investigated Jurassic limestones and Triassic marls in the Italian Maritime Alps. However, IP variations in limestones have not been frequently investigated in previous research.…”

A multidisciplinary geological and geophysical approach to define structural and hydrogeological implications of the Molinaccio spring (Spello, Italy)

“…The ERT technique was widely used for the detection of resistivity differences originated by faults and tunnels, as shown in literature e.g. by Chambers et al (2006), Gelis et al (2010) and Ortega et al (2010).…”