AEM-derived watersheds in crystalline domain under volcanic cover

International audienceIn the Chaîne des Puys (CdP, France), volcanic edifices and their emissions cover the weathered conductive low-permeable basement and fill the paleo-valleys, hiding the groundwater flows. The 3D delineation of such buried watersheds can be achieved studying variations of conductivity related to primary geological contrasts as well as secondary weathering-induced contrasts.We used AEM data to delineate the geometry of the undercover volcanism-basement interface in the northern part of the CdP and derived watersheds. Despite the highly resistive volcanic cover, our processing allowed structural imaging up to a depth of investigation of 330 meters in average.The processing and inversion of AEM data highlights the interface between a strongly resistant volcanic cover (~104-105 Ω.m) and a decametric conductive weathered horizon at the top of the basement (30-300 Ω.m).We picked the weathered horizon of the basement on several resistivity profiles, to build an elevation model of its top. The newly derived watersheds noticeably differ from the ones proposed in literature