GNGTS 2014 - Atti del 33° Convegno Nazionale

26 GNGTS 2014 S essione 1.1 A reappraisal of the 1783 seismic sequence and related seismogenic faults in the Calabrian Arc (southern Italy M.S. Barbano, C. Pirrotta Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Catania, Italy Introduction. According to the most recent earthquake Italian catalogues, five devastating earthquakes struck the southern Calabria between February 5 and March 28, 1783 (Boschi et al. , 2000; Rovida et al. , 2011). ��� ���� �������� ������ � ���������������� ������ ���� ������� The 1783 sequence caused a geomorphological crisis that changed the Aspromonte and Serre Mts landscape triggering ground fracturing, deep seated gravitative deformations, landslides, liquefactions and inducing a substantial change in the fluvial network geometry with deviation and dam of fluvial channels, as well as the development of numerous lakes and other hydrological anomalies (Cotecchia et al. , 1996). Several authors deal with these earthquakes for different purposes such as earthquake catalogues, tsunamis and seismogenic fault individuation (e.g., Boschi et al. , 2000; Graziani et al. , 2006; Jacques et al. , 2001; Galli and Bosi, 2002). There is a general agreement that some of the 1783 earthquakes are associated with the main NE-SW striking west-dipping active swarm of normal faults running along the Calabrian Arc. This hypothesis is also supported by the present-day WNW-ESE-trending crustal extension documented by focal mechanisms of earthquakes (CMT and RCMT Catalogues; Neri et al. , 2004), geodetic deformation velocities (Mattia et al. , 2009; D’Agostino et al. , 2011) and structural studies (Tortorici et al. , 1995; Jacques et al. , 2001; Ferranti et al. , 2008). Nevertheless some of the events are not associated with faults and some sources are not well defined. Although a lot of coeval reports are available for the 1783 seismic sequence, the overlap of many shocks in very narrow time and space makes the interpretation of historical data difficult, because historical accounts describing damage in several localities do not distinguish the shocks. An accurate revision of the 1783 seismic crisis has been carried out with the main purpose of better separating the effects of the different shocks and understanding the seismogenic faults associated with these earthquakes. We show results for some minor shocks, whereas for the main five shocks we report published data. The 1783 seismic sequence: a reappraisal. The devastating seismic sequence occurred in Calabria and in northeastern Sicily started on February 5 and was followed by a long series of earthquakes that migrated from the Messina Strait toward NNE, along the axis of the Calabrian Arc. The aftershocks lasted for about ten years. More than 180 localities were totally destroyed or almost collapsed and there were more than 30,000 victims. Historical sources, testifying the effects of the 1783 earthquakes, come from different kinds of documents: chronicles, newspapers and reports (for a comprehensive reference list see Boschi et al. , 1995). Among the numerous sources, the most complete works are those of Sarconi (1784), Vivenzio (1783, 1788) and De Dolemieu (1784). The first is the final report of the mission sent by the Bourbon government in Calabria and Messina for a systematic survey of the damaged sites, the second holds assembled data from several accounts and the third is the report of observations made during Dolemieu’ trip in Calabria between February and March 1784. There are also several useful memoirs describing detailed effects in single locations, as well as dates and hours for felt shocks (Fig. 1), such as Corrao (1784), Gallo (1783, 1784) and Torreani (1784) for Messina, Roscitano (1783) and Palestino (1895) for Reggio Calabria, Minasi (1783, 1785) for Scilla; Masci (1783) for Santa Sofia, Serrao (1785) for Castelmonardo, De Leone (1783) and Augusti (1784) for Catanzaro and Vivenzio (1788) for Monteleone. In order to separate shocks, we analyzed the description for single localities and compared the corresponding with the felt time of other sites. After having unraveled a tangle of multiple dates, hours and spurious connections between several earthquakes we identified collections of historical data dealing with single seismic events. This analysis allowed identifying more events than the five destructive shocks usually reported for the 1783 catastrophe.