GNGTS 2014 - Atti del 33° Convegno Nazionale

68 GNGTS 2014 S essione 1.1 “Mercure” event in 1998 (Brozzetti et al. , 2009). The Parametric Catalogue of Italian earthquakes (CPTI11, Rovida et al. , 2011), shows very well the lack of strong earthquakes in the region: there is a clear evidence of large earthquakes in the Campania-Basilicata area (M~7.0) and several strong earthquakes in the Sila region and in the whole Calabrian territory. According to the seismic classification of the national territory, the area affected by the 2010-2014 seismic activity have a relatively higher probability to be shaken by a strong acceleration (Gruppo di Lavoro MPS, 2004). Most of the seismic events occurred in areas where the peak ground acceleration having 10% chance of being exceeded in next 50 years is between the values of 0.225 g and 0.275 g. The 2010-2014 seismic activity and the temporary seismic networks. Between 2010 and 2014 the Italian Seismic Network (Amato and Mele, 2008) detected about 6000 earthquakes in the study area (Italian Seismological Instrumental and Parametric Data-Base ISIDE Working Group, 2010; ISIDe .rm.ingv.it ; Fig. 1). The seismicity shows an unusual spatio-temporal pattern (Passarelli et al. , 2012): swarm like activity and mainshock-aftershock sequences coexist. In 2011 the earthquake rate has been variable, with increasing and decreasing phases and maximum magnitudes below M L =4.0. On May 28, 2012, a shallow event with local magnitude M L =4.3 struck about 5 km E of the previous swarm. The seismic activity remained concentrated in the M L =4.3 source region until early August showing a mainshock-aftershock behaviour. At that time seismicity jumped back westward to the previous area, with several earthquakes of local magnitude larger than 3.0, culminating with a M L =5.0 earthquake on October 25, 2012. The seismic rate remained high for some months, but magnitudes did not exceed 3.7. The seismic rate suddenly decreased at the beginning of 2013 and stayed quite low for the rest of the year up to June 2014 when a magnitude 4.0 occurred in the eastern cluster. The fault plane solutions identified by the Time Domain Moment Tensor (TDMT; http://cnt.rm.ingv.it/tdmt. html; Scognamiglio et al., 2009) for the two major events are consistent with normal faults trending ~N20W and dipping at about 45°. During these years several temporary seismic stations were deployed in the area (Fig. 2).After the increasing of seismic moment release in November 2011, the Centro Nazionale Terremoti of INGV, in collaboration with the Dipartimento di Fisica dell’Università della Calabria, improved Fig. 1 – Daily number of earthquakes localized by the INGV monitoring survey in the Pollino region from January 2010 to August 2014 and the number of temporary stations deployed in the area. The * refers to the seismic array deployment.