A M_W 6.3 earthquake struck on April 6, 2009 the Abruzzi region (central Italy) producing vast damage in the L'Aquila town and surroundings. In this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks. The distribution of aftershocks, 712 selected events with M_L ≥ 2.3 and 20 with M_L ≥ 4.0, defines a complex, 40 km long, NW trending extensional structure. The main shock fault segment extends for 15–18 km and dips at 45° to the SW, between 10 and 2 km depth. The extent of aftershocks coincides with the surface trace of the Paganica fault, a poorly known normal fault that, after the event, has been quoted to accommodate the extension of the area. We observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes.