Electrical Resistivity Tomography (ERT) Applied to the Characterization of Fractured and Weathered Zones in Subsurface Granites

Two ERT campaigns were carried out to characterize the subsurface geology and the possible infiltration and flow pathways of the water through the granites (fractured and weathered zones) from the Barranc de Contraix area (Aiguestortes i Estany de Sant Maurici National Park, Catalonia, NE Iberian Peninsula). Three types of geoelectric levels were defined: high resistivity levels (>15.000 Ω-m), medium resistivity levels (between 6.000 and 15.000 Q-m) and low resistivity levels (<6.000 Ω-m). The ERT profiles have been shown highly resolutive to identify the existence of these fractured and/or weathered zones on the granites, represented by relatively low resistivities in comparison with the high resistivities associated to fresh granites. This fractured or weathered zones on the granites may allow the flow of water from the high mountain lakes Estanys Gelats (>2700 m.a.s.l.) to the actual fluvial system (1900 m.a.s.l.).