The April 2009 Aquila (central Italy) seismic sequence (Mw6.3): A preliminary seismotectonic picture,

Abstract

On April 6, 2009, an Mw 6.3 earthquake struck the town of L’Aquila in the Abruzzo region in central Italy. It was followed by a long seismic crisis with other four events with Mw between 5.1 and 5.6. Seismological and geological data point out an upper crust extensional stress field with an average WSW-ENE tensional axis. In the course of the seismic sequence, two distinct en échelon fault sources were activated: first, the SW-dipping Paganica normal fault, which is associated with the Mw 6.3 event; and, subsequently, the southern part of the WSW-dipping Gorzano normal fault.Co-seismic ground deformation (open fissures, en échelon cracks and shear planes with centimetric downthrows) was surveyed for ~ 13 km along the Paganica fault. The integration of the information from this last Italian earthquake with the previous seismotectonic background has allowed us to further detail the 3-D shape and the size of some of the individual seismogenic sources of the Apennine active extensional belt.