New insights into the High Agri Valley deep structure revealed by magnetotelluric imaging and seismic tomography (southern Apennine, Italy)

We present an electrical resistivity model obtained from a 2D Magnetotelluric survey across a large sector of the Southern Apennine in the High Agri Valley (HAV), a NW-SE trending intra-mountain basin, with a high seismogenic potential. The intensive hydrocarbon exploitation (Val d'Agri oilfield) makes this area also affected by induced seismicity. In this HAV sector, the injection of salt-water in an unproductive disposal well (Costa-Molina2) causes localized swarms of microearthquakes; a second cluster of continuous induced seismicity is also observed SW of the Pertusillo Lake and it is associated to the seasonal fluctuations of the reservoir's water level. The major insight inferred from this study concerns a better understanding of the geological and tectonic framework in the HAV. The electrical resistivity model images the subsurface as conductive sedimentary sequences (Allochthonous Units) upon the carbonate Apulian Platform Unit characterized by higher resistivity values. Both these units appear composed of thrust-and-fold system deepening with larger wavelength anticlines N-E towards. Most of the structures identified in the magnetotelluric model are rather superficial and confined within the Allochthonous Units. A sudden break of the Apulian platform under the central part of the MT profile defines a conductive zone possibly associated to a major SW-dipping reverse fault or to several branches, as closely spaced thrust-sheets cutting eastern flanks of the Agri Valley