L'Aquila (Central Italy) Earthquakes: The Predecessors of the April 6, 2009 Event

On 6 April 2009 an Mw = 6.3, Imax = 9–10 earthquake struck the Abruzzi region of Central Italy (http://portale.ingv.it/highlights/view?set_language=en). We find similarities in some peculiar characteristics of the 2009 sequence and some historical events that occurred in the area, in particular in 1461 and 1762. We observed strong analogies in the distribution of the intensities and in the areas of the strongest effects produced by these shocks, as well as in the temporal evolution of the events. The 2009 quake severely devastated the town of L'Aquila (∼ 73,000 inhabitants) and tens of villages located in the middle Aterno Valley (hereinafter MAV, see Figure 1). One month after the event, its social impact was not yet fully known but was certainly burdensome: 308 casualties, 47% of homes damaged in the epicentral area, 20% of those were heavily damaged (with an even worse situation in downtown L'Aquila), and about 40,000 people left homeless. Although the magnitude of the event was not among the largest to have occurred in the Apennines, the Abruzzi earthquake can be considered one of the most disastrous of the last century. The effects of the shaking were recorded not only in the epicentral zone but also in distant areas ( e.g. , as far as Rome, some 90 km from the epicenter, where it produced light damage) and heavily affected the cultural and socio-economic fabric of a wide region characterized by high seismic risk. The present tectonic regime of the Abruzzi sector of the Apennines is characterized by Quaternary normal faults striking NW-SE or N-S. During the evolution of the chain, the activity of the main normal faults led to the formation of intermontane extensional basins filled with Pliocene-Quaternary deposits (Carraro and Giardino 1992; Calamita and Pizzi 1994). These faults are responsible for some of the strongest …