GNGTS 2014 - Atti del 33° Convegno Nazionale

30 GNGTS 2014 S essione 1.1 The February 7 damage distribution clearly suggests the activation of the Mesima fault (e.g. Tortorici et al. , 1995). The magnitude estimated from intensity is 7.0 (Rovida et al. , 2011). The relationship between the February 27, March 1 and March 28 1783 damage and the near known faults is poorly understood. The March 1 event appears to be linked also to a further north rupture of the Mesima fault. Whereas the 28 March 1783 macroseismic distribution is widely scattered; it is evident from the large felt area and the small gradient between different intensities that the last quake had a deeper source with respect to the previous events. This observation can account for the lack of coseismic rupture. The magnitude estimate for this event is 6.8-7.0 (Rovida et al. , 2011). The intensity distribution suggests an E-W oriented fault, therefore it is likely linked to one of the strike-slip faults of the Catanzaro basin (Ghisetti and Vezzani, 1982).The Lamezia-Catanzaro fault (Fig. 2) suggested by Moretti (1982) seems to be far from the maximum damaged area and therefore it is like that the seismogenic structure of this quake should be searched southernmost. The April 27 and 28 shocks that damaged Milazzo seem to be related with a Sicilian source probably the Tindari fault. Lastly the 30 July shock may be associated with one of the Ionian faults that did not slipped during previous earthquakes. Conclusion. The analysis of the 1783 sequence highlights that macroseismic fields of the single event can be overestimated because earthquakes occurred close in space and time and observed damage is the cumulative effects of multiple events. Furthermore effects observed in some localities are reported for the strongest events, but they could be due to minor earthquakes. During the 1783 seismic sequence ruptured both Apennine structures and transversal faults. Most of earthquakes are linked to Apennine structures but, at the end of the main sequence, transversal structures ruptured as well. In this framework, the role played by the transverse structures is fundamental in limiting the extension of the main faults. The March 28 earthquake may be associated to a stress transfer toward larger depth, where accumulated stress is slowly released because rheological properties at deepest levels retard slips. The 1783 seismic sequence seems to be like, apart from the highest magnitudes, to the 1997-98 central Italy seismic sequence (Mw = 5.9). Indeed most of the Umbria-Marche earthquakes occurred along Apennine structures, but when seismic activity decreased, in March 26, 1998 a Mw = 5.3 deeper event occurred. The epicentre of this shock was located at the northern end of the Apennine faults associated with the Umbria-Marche seismic sequence, at a depth of 46.6 km (Pino and Mazza, 2000). References Augusti M.; 1783: Dei terremoti di Messina e di Calabria dell’anno 1783, memorie e riflessioni. �������� Bologna. BarbanoM.S., CastelliV., PantostiD., PirrottaC.; 2014: Integrationof historical,archaeoseismicandpaleoseismological data for the reconstruction of the early seismic history in Messina Strait (south Italy): the 1st and 4th centuries AD earthquakes. Ann. Geoph., 57 (1), S0192. Basili R., Valensise G., Vannoli P., Burrato P., Fracassi U., Mariano S., Tiberti M.M., Boschi E.; 2008: The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research on Italy’s earthquake geology. ��������������� ������������������������������� Tectonophysics, doi:10.1016/j.tecto.2007.04.014 Boschi E., Ferrari G., Gasperini P., Guidoboni E., Smriglio G., Valensise G.; 1995: Catalogo dei forti terremoti in Italia dal 461 a.C. al 1980, ING-SGA, Bologna, 973 pp. e CD-ROM. Boschi E., Guidoboni E., Ferrari G., Gasperini P., Mariotti D., Valensise G. (eds.); 2000: Catalogue of Strong Italian Earthquakes from 461 B.C. to 1997, Ann. Geof., 43, 609-868. Corrao A.; 1784: Memoria sopra i tremuoti di Messina accaduti nell’anno 1783, Messina Cotecchia V., Guerricchio A., Melidoro G.; 1986: The geomorphogenetic crisis triggered by the 1783 earthquake in Calabria (southern Italy). Proc. International Symposium on “Engineering Geology Problems In Seismic Areas”, 6, 245-304, Bari, 13-19 April. D’Agostino N., D’Anastasio E., Gervasi A., Guerra I., Nedimović M. R., Seeber L. and Steckler M.; 2011: Forearc extension and slow rollback of the Calabrian Arc from GPS measurements, Geophys. ���� ������ ��� ������� Res. Lett., 38, L17304. De Dolomieu D.; 1784: Mémoire sur le Tremblement de Terre de la Calabre Pendant l’Année 1783. �������� ����� Fulgoni, Rome. De Leone A.; 1783: Giornale de’ tremuori accaduti l’anno 1783 nella provincia di Catanzaro, Napoli. De Lorenzo A.; 1895: Un secondo manipolo di monografie e memorie reggine e calabresi, Siena.