Coseismic and post-seismic slip of the 2009 L'Aquila (central Italy) MW 6.3 earthquake and implications for seismic potential along the Campotosto fault from joint inversion of high-precision levelling, InSAR and GPS data

Abstract

After the April 6th 2009 MW 6.3 (ML 5.9) L'Aquila earthquake (central Italy), we re-measured more than 100 km of high-precision levelling lines in the epicentral area. The joint inversion of the levelling measurements with InSAR and GPS measurements, allowed us to derive new coseismic and post-seismic slip distributions and to de- scribe, with high resolution details on surface displacements, the activation and the slip distribution of a second- ary fault during the aftershock sequence that struck the Campotosto area (major event MW 5.2). Coseismic slip on the Paganica fault occurred on one main asperity, while the afterslip distribution shows a more complex pattern, occurring on three main patches, including both slips on the shallow portions and on the deeper parts of the rup- ture plane. The comparison between coseismic and post-seismic slip distributions strongly suggests that afterslip was triggered at the edges of the coseismic asperity. The activation of a segment of the Campotosto fault during the aftershock sequence, with a good correlation between the estimated slipping area, moment release and distribution of aftershocks, raises the opportunity to discuss the local seismic hazard following the occurrence of the 2009 L'Aquila mainshock. The Campotosto fault appears capable of generating earthquakes as large as his- torical events in the region (M N 6.5) or as small as the ones associated with the 2009 sequence. In the case that the Campotosto fault is accumulating a significant portion of the current interseismic deformation, the 2009 MW N 5 events will have released only a small amount of the accumulated elastic strain, and then a significant hazard still remains in the area. Continuing geodetic monitoring and a densification of the GPS networks in the region are therefore needed to estimate the tectonic loading across the different recognized active fault systems in this part of the Apennines.