Terra Nova, 25, 21–29, 2013


How reliably can a seismogenic fault be identified in complex tectonic settings such as the Italian Apennines? The aftershocks of the Mw 6.3, 2009 L'Aquila earthquake developed both on the primary seismogenic fault and on a northwestern, adjacent segment. Here, the active Gorzano normal fault is exposed, and many seismogenic models are based on it. Compared with the tectonic setting, however, the 2009 aftershock sequence shows that the deep seismogenic fault does not correspond with the exposed fault plane. The latter flattens at a depth of ∼4 km, and is totally hosted within a 6–7 km-thick thrust sheet. The 2009 earthquake sequence, instead, depicts an independent fault in a deeper thrust sheet. The Gorzano fault is kinematically reactivated only at the hangingwall of the deeper fault. In complex tectonic settings, seismogenic faults can be properly characterized only through the joint analysis of many independent geological and geophysical data.