Complementarity of Electrical Resistivity Tomography and Ground Penetrating Radar to Study Karst Unsaturated Zone
Résumé
The structure of karst hydrosystems is complex and the related hydrodynamic functioning mechanism can be highly heterogeneous in both unsaturated and saturated zones. The Low-Noise Underground Laboratory of Rustrel (LSBB) is located in unsaturated zone (UZ) of Fontaine de Vaucluse (FdV) karst hydrosystem. In this way, the LSBB is a unique place to apply surface-based geophysical surveys due to numerous and various geological and hydrogeological knowledge under the investigated zone. We exhibit in this paper complementarity and efficiency of Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR). Both GPR and ERT are well suited for the first phase of our study, in order to characterize the general structure of the investigated chosen zone. GPR results highlight the tectonic features which are also, but less accurately, seen by ERT apparent resistivity maps. ERT 2D inverted results have shown the presence of moderate resistivity zones within the limestone. The provided information allowed carrying out following step of our study to enhance understanding of local karst UZ e.i. apply Magnetic Resonance Sounding (MRS), Gravimetry and Low Frequency Electromagnetics (LF-EM).