Electrical imaging of the April 2009 L'Aquila earthquake fault (Mw=6.3, central Italy)

The April 6, 2009 L'Aquila event (epicentral intensity Io=9 MCS, 308 casualties) has been characterized by a Mw=6.3 and by a coseismic rupture of about 18 km along the NW-SE trending Paganica-San Demetrio fault system. The earthquake enucleated just below the L'Aquila town at a depth of 9 km, rupturing then toward SE, as showed by instrumental and macroseismic data. The Paganica-San Demetrio structure includes several 1-to-5-km long normal fault segments, with a dextral en-echelon geometry; surficial breaks were observed all along its entire length, with a maximum vertical offset of 10 cm. Due to the high urbanization of the area, which often erased the faint trace of the fault at surface, and in order to imaging the first metres of the fault at depth, we performed four Electrical Resistivity Tomography (ERT) across the Paganica segment. In order to test the different sensibility of the arrays with respect to the specific geological conditions and research goals, the electrical tomographies have been acquired using a multielectrode system with different electrode spacing and with different arrays (dipole-dipole, Wenner and Wenner-Schlumberger). Results showed clearly the long-term cumulated effect of the fault at depth, allowing thus the precise location of paleoseimological trenches which were successfully dug