GNGTS 2011 SESSIONE 1.1 loghi CPTI08/CFTI4 e di rivedere la valutazione delle intensità assegnate secondo la scala EMS98. Quest’ultima operazione è stata svolta con una sistematica e minuziosa rilettura delle descrizioni di danni, organizzata attraverso l’omogeneizzazione dei termini usati per descriverli e integrata con gli elementi necessari per ricostruire l’assetto urbanistico degli insediamenti colpiti in base alla loro consistenza numerica, tipologia edilizia, vulnerabilità. La disamina delle fonti porta ad assegnare una Imax 9 EMS alla sola località di Castelnuovo, mentre per altre sette località risulta un’intensi- tà ben al di sopra della soglia del danno. La magnitudo macrosismica calcolata con il codice Boxer 4.0 (Gasperini et al., 2010) è pari a Mw 5.5. Al termine dello studio il terremoto del 6 ottobre 1762 risulta considerevolmente arricchito per quanto riguarda il quadro complessivo delle conoscenze e lievemente ridimensionato sia nella magnitudo sia nella intensità massima raggiunta; la distribuzione delle intensità è probabilmente “viziata” da effetti locali, a conferma di quanto già emerso in precedenti studi (Lanzo et al., 2011). L’ipotesi che l’evento del 1762 possa essere stato un predecessore (Tertulliani et al., 2009) di quel- lo del 2009 sembra da riconsiderare, risultando più credibile che si sia trattato di un evento collo- cato su un segmento di faglia più meridionale. Più in generale, l’esperienza fatta con questo studio ci conferma che anche in zone ad alta sismicità dove i terremoti sono noti e ben documentati, dopo decenni di studi di sismologia storica, il margine di miglioramento delle conoscenze può essere, in certi casi, ancora ampio. Bibliografia Gasperini P., Vannucci G., Tripone D., and Boschi E.; 2010: The location and sizing of historical earthquakes using the attenuation of macroseismic intensity with distance, Bull. Seismol. Soc. Am., 100, 2035–2066, doi: 10.1785/0120090330. Gruppo di lavoro CPTI; 2009: Catalogo Parametrico dei Terremoti Italiani, versione parziale “CPTI08aq”, a cura di A. Rovida, http://emidius.mi.ingv.it/CPTI08. Guidoboni E., Ferrari G., Mariotti D., Comastri A., Tarabusi G. and Valensise G.; 2007: CFTI4Med, Catalogue of strong earthquakes in Italy (461 B.C.-1997) and Mediterranean area (760B.C.-1500), http://storing.ingv.it/cfti4med Tertulliani A., Rossi A., Cucci L., Vecchi M.;2009: L’Aquila (Central Italy) earthquakes: the predecessors of the April 6, 2009 event, Seism. Res. Lett. 80, 6, 1008-1013, doi: 10.1785/gssrl.80.6.1008. Lanzo G., Silvestri F., Costanzo A., d’Onofrio A., Martelli L., Pagliaroli A., Sica S., Simonelli A.; 2011: Site response studies and seismic microzoning in the Middle Aterno valley (L’Aquila, Central Italy), Bull. Earthquake Eng., 9, 1417–1442, DOI 10.1007/s10518-011-9278-y. ACTIVE TECTONICS ALONG THE NEBRODI-PELORITANI BOUNDARY (NE SICILY): A NEW POTENTIAL SEISMOGENIC SOURCE S. Catalano, F. Pavano, G. Romagnoli, G. Tortorici Dipartimento di Scienze Geologiche, Università di Catania Introduction. In NE Sicily, the geodetic data (Hollenstein et al., 2002) indicate the occurrence of a crustal sector that diverges from the rest of the Sicily. Several sites located in the Nebrodi- Peloritani Mountains and the Eolian Islands, in fact, show N-ward directed GPS vectors that, if combined with those of the rest of the Sicily, pointing towards the NW, would constrain a NNE- SSW oriented active extension, at rate of about 4.5 mm/a (inset in Fig. 1). This evidence conflicts with the available geological data, reporting for the Nebrodi-Peloritani Boundary diffuse Plio-Pleis- tocene NW-SE oriented dextral faults, associated with NE-SW oriented thrust and folds and E-W oriented oblique thrust (Ghisetti & Vezzani, 1982; Lentini et al., 2000). A morphostructural study, based on analyses of 1:10,000 and 1:33,000 scale aerial photographs and satellite images and field analyses of the terraced deposits, has been carried out along the Tyrrhenian coast of NE Sicily in order to recognize the location and the geometry of the tectonic margin that separates the diverging crustal domains. The study has been integrated with mesoscale kinematic analyses on fault planes. The aim of the study is to define the displacement-rate and the related seismogenic potential that can be released along this active extensional boundary. Marine terraces and tectonic uplift in NE Sicily. The Tyrrhenian coast of the NE Sicily is bordered by a flight of Late Quaternary marine terraces, which is composed by several polycyclic 28 GNGTS 2011 SESSIONE 1.1 surfaces that ranges from the OIS 15 (570 ka) to the OIS 3 (60 ka) (Catalano & Di Stefano, 1997) (Tab. 1). The tectonic uplifting of the region post-dates the deposition of the Early-Middle Pleistocene (900-600 ka) marine sequence that now crops out at an elevation of about 580 m a.s.l., in the area of the Naso village, near Capo d’Orlando (Fig. 1). The present elevation of these deposits, corrected for their depth of deposition, constrain a total vertical displacement of about 680 m, in the last 600 ka. This implies an averaged uplift-rate of about 1.1 mm/a. This estimation is consistent with the vertical displacement of the strandlines of the marine terraces that indicates an almost uniform uplift-rate (1.1 ± 0.05 mm/a), constant for the entire 80 km-long segment of the coast, from Messina to Capo d’Orlando (Tab. 1). Tab. i - Marine terraces. A sharp decrease in the elevation of the strandlines of the marine terraces has been recognised in the coast between Capo d’Orlando and S. Marco d’Alunzio (Fig. 1). In this segment of the coast, a single marine platform represents each of the OISs from 13 (520 ka) to 7 (240 ka). A polycyclic abrasion surface has been recognised only for the OIS 5 (125-80 ka), while the marine terrace of the OIS 3 (60 ka) has been cancelled by the retreat of the Holocene sea-cliff (tab 1). The elevation of the strandlines in the S. Marco d’Alunzio section indicate an averaged uplift-rate of about 0.7 mm/a, almost constant in the last 520 ka. This implies that a relative vertical motion of about 0.4 ± 0.05 mm/a could be related to the occurrence of active tectonics in the region between Capo d’Or- lando and S.Marco d’Alunzio Quaternary tectonics in the Capo d’Orlando-San Marco d’Alunzio region. In the region between S. Marco d’Alunzio and Capo d’Orlando (Fig. 1) Early-Middle Pleistocene deposits, com- posed of basal calcarenites evolving to batial marly clays (Catalano & Di Stefano, 1997), culminate in the hill of Naso. Along the southwestern slope of this culmination, discrete segments of a NW- SE oriented dextral shear zone have been reactivated by extensional motions, generating the Naso Fault Zone (NFZ in Fig. 1). The normal faulting has involved the deposits of the Pleistocene marine succession, whose basal levels are downthrown towards the southwest, for about 40 m. The verti- cal motion along the fault zone has been associated with the deposition of syn-tectonic slope deposits that consist of a prevalent sandy matrix, including metric blocks of the Pleistocene cal- carenites. These deposits, which drape ancient fault scarps, being involved by the later normal fault motions (Fig. 2), are terraced along an outer-edge that, resting at an elevation of about 130 m a.s.l., can be correlated, towards the coast, with that of the Tyrrhenian (125-80 ka) polycyclic abrasion surface. The normal fault segments located to the south of Naso are concealed by a thick Recent 29 GNGTS 2011 SESSIONE 1.1 Fig. 1 - Active tectonics and Pleistocene deposits at the Nebrodi-Peloritani Boundary. The focal mechanism of the 06.23.2011 event is from ISIDe Working Group (INGV, 2011). 30 GNGTS 2011 SESSIONE 1.1 Fig. 2 - Panoramic view of the free face along the SFZ (a); Detail of the free face, showing a basal light-coloured strips, along the SFZ (b); Late Pleistocene slope deposits displaced along the NFZ (c). (Holocene) talus that draps graded slope profile. More to the south, in the area running from S. Mar- co d’Alunzio to Galati Mamertino, a further NW-SE oriented, 8.5 km-long, fault zone (San Marco d’Alunzio Fault Zone; SFZ in Fig. 1) is composed of several discrete NW-oriented fault segments, showing well defined rejuvenated scarps as an evidence of their Holocene activity. The remobilised fault segments range in length from 1 to 4 km. The longest segment, located between the villages of Frazzanò and S.Marco d’Alunzio (Fig. 1), is characterised by a 3-5 m high, SW facing fresh bedrock scarp, marked at the base by a light coloured strip (Fig. 2). Kinematic indicators observed on the fault plane constrain a normal sense of motion (pitch= 80°). This normal fault is associated with a minor 2 km-long antithetic segment, marked by a 3 m-high rejuvenated scarp. This antithet- ic fault is characterised by striations indicating a normal (pitch= 80°) sense of motion, superimposed on ancient indicators of dextral movement (pitch= 160°). More to the south, further four NW-SE oriented segments, showing 2 m-high fresh bedrock scarps have been recognised. Between the vil- lages of Galati Mamertino and Tortorici (Fig. 1), two SW dipping steep scarps extends for about 1500 m and 800 m, respectively. Between Longi and the Catafulco Gorge, two antithetic, NE fac- ing fresh scarps have been recognised for length of 500 m and 1500 m, respectively. Finally, to the southwest of Tortorici, two measurement sites have been located along a N10 ori- ented, E-dipping, 1600 m long fresh bedrock scarp.