The Paganica Fault and Surface Coseismic Ruptures Caused by the 6 April 2009 Earthquake (L'Aquila, Central Italy)

Abstract

On 6 April 2009, at 01:32 GMT, an Mw 6.3 seismic event hit the central Apennines, severely damaging the town of L'Aquila and dozens of neighboring villages and resulting in approximately 300 casualties (Istituto Nazionale di Geofisica e Vulcanologia, http://www.ingv.it; MedNet, http://mednet.rm.ingv.it/procedure/events/QRCMT/090406_013322/qrcmt.html). This earthquake was the strongest in central Italy since the devastating 1915 Fucino event ( Mw 7.0). The INGV national seismic network located the hypocenter 5 km southwest of L'Aquila, 8–9 km deep. Based on this information and on the seismotectonic framework of the region, earthquake geologists traveled to the field to identify possible surface faulting (Emergeo Working Group 2009a, 2009b). The most convincing evidence of primary surface rupture is along the Paganica fault, the geometry of which is consistent with seismological, synthetic aperture radar (SAR) and GPS data. Investigation of other known normal faults of the area, i.e. , the Mt. Pettino, Mt. San Franco, and Mt. Stabiata normal faults suggested that these structures were not activated during the April 6 shock (Emergeo Working Group 2009a, 2009b). In this report, we first describe the seismotectonic framework of the area, and then we present the field information that supports the occurrence of surficial displacement on the Paganica fault. The shock of 6 April 2009 occurred in a region that has been struck by past earthquakes (CPTI Working Group 2004; Figure 1) and is in an Apennine sector that contains a complex array of active normal faults ( e.g. , Barchi et al. 2000; Galadini and Galli 2000; Boncio et al. 2004; Roberts and Michetti 2004). In the central Apennines, active faulting and earthquakes result from the ongoing extensional tectonics. The strongest earthquakes in the CPTI04 seismic catalog (CPTI Working Group 2004) occurred on 9 September 1349 ( Mw 6.5) and 2 February …