GNGTS 2016 - Atti del 35° Convegno Nazionale

88 GNGTS 2016 S essione A matrice Effective decoupling of surface and deep tectonics and seismic hazard implications: excerpts from the 2016 Amatrice, 2009 L’Aquila, and 1997 Colfiorito earthquakes (central Italy) G. Valensise 1 , P. Vannoli 1 , R. Basili 1 , L. Bonini 2,1 , P. Burrato 1 , M.M.C. Carafa 3 , U. Fracassi 1 , V. Kastelic 3 , F.E. Maesano 1 , M.M. Tiberti 1 , G. Tarabusi 4 1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 1, Roma, Italy 2 Dipartimento di Matematica e Geoscienze, Università di Trieste, Italy 3 Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 1, L’Aquila, Italy 4 Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 1, Bologna, Italy On August 24, 2016, a M w 6.0 earthquake devastated a portion of the central Apennines near Amatrice, causing nearly 300 victims and substantial property damage. The earthquake occurred in an especially well monitored region, such that it has taken just a few days to realize that, although sharing the general characteristics of other Apennines extensional events, the Amatrice earthquake exhibits peculiarities that are quite surprising for many earthquake geologists. Once again they were confronted with a complex rupture, too deep and too shallow- dipping to connect with the active faults known in the region, and breaking through the Monti Sibillini Thrust, considered by many to be a major regional tectonic - and segment - boundary. The August 24, 2016 earthquake is the last of a string of three disastrous, similarly-sized earthquakes (Fig. 1), all caused by normal faulting along planes dipping 40°-50° to the southwest, as shown by their characteristic InSAR signature (Fig. 2), and all of which occurred along the crest of the central Apennines. The 2016 sequence follows the April 6, 2009 L’Aquila earthquake (M w 6.3), with its strong 9April aftershock in the Campotosto-Monti della Laga area (M w 5.4) (e.g. Valoroso et al. , 2013), and the 26 September and 14 October, Colfiorito-Sellano earthquakes (M w 5.7, 6.1 and 5.6) (e.g. Chiaraluce et al. , 2005), respectively located to the southeast and to the northwest of Amatrice along the axis of the central Apennines (Fig. 1). These earthquakes delineated a tectonic style that is largely in contrast with the views on the active tectonics of the central Apennines that dominated the scientific debate of the past thirty years [this topic is extensively discussed in Vannoli et al. (2012) and Bonini et al. (2014)]. We discuss the important lessons that can be learned from the Amatrice earthquake and its predecessors, focusing on their implications for an improved assessment of the regional seismic hazard. These three earthquake sequences share the availability a) of numerous and reliable data collected by the permanent INGV network and by temporary networks, and b) of good quality InSAR data. The Fig. 1 – Geographic setting and seismogenic sources discussed in text. Presumed active fault from various sources are shown in red. Sources in green are taken from the DISS database (DISS Working Group, 2015). The two sub-sources proposed for the 2016 earthquake, in purple, are modified from Gruppo di Lavoro IREA& INGV (2016). A dark dashed line shows the regional watershed.