GNGTS 2014 - Atti del 33° Convegno Nazionale

the Umbrian Apennines, more than 400 events have already occurred in the first six months of 2014, so that at the end of this year the total number of events could considerably overcome the one of 2013. In the case of the L’Aquila seismic crisis, the remarkable increase of background seismicity began about 4 months before the main shock (April 6, 2009) and involved about 300 events of M >2. Considering that in the Gubbio basin the period of increased background activity is now longer than 15 months, and has already produced more than 800 events, this possible premonitory signal could be taken into account for managing eventual initiatives for seismic risk mitigation. Conclusions. It is argued that the major seismic zone that characterizes the Tuscany-Umbria Apennines (Norcia-Colfiorito-Gualdo Tadino-Gubbio-Alta Valtiberina) has been generated by the divergence between the outer sector of the RMU wedge and the inner belt, driven by the belt parallel compression in the outer sector of the chain induced by the Adriatic plate. This interpretation and the related kinematic pattern (Fig. 1) is compatible with the present velocity field deduced by geodetic observations (Fig. 2). The proposed tectonic mechanism in the study area is mainly favoured by the seismic activation of the zones surrounding the easternmost wedge of the Lazio-Abruzzi platform (Gran Sasso Arc), which have developed, by a number of major shocks (M>5.5) in the recent seismic history (since 1930). This context could imply that the NCGGA fault system is now more prone to next major shocks with respect to the other seismic zones of the northern Apennines. Another signal in this direction is given by the fact that background seismic activity in the above system has been anomalously high in the last 2 years. References Ascione A., Caiazzo C., Cinque A.; 2007: Recent faulting in Southern Apennines (Italy): geomorphic evidence, spatial distribution and implications for rates of activity . ����� ���� ����� ��� ���� �� ������������� Boll. Soc. Geol. It. (It. J. Geosciences), 126 , 293-305. Cenni N., Mantovani E., Baldi P., Viti M.; 2012: Present kinematics of Central and Northern Italy from continuous GPS measurements . �� ������������ J. Geodynamics, 58 , 62-72. Cenni N., Viti M., Baldi P., Mantovani E., Bacchetti M.,Vannucchi A.; 2013: Present vertical movements in central and northern Italy from GPS data: possible role of natural and anthropogenic causes . J. Geodynamics, 71 , 74- 85. Finetti I.R., Boccaletti M., Bonini M., Del Ben A., Pipan M., Prizzon A., Sani F.; 2005: Lithospheric Tecton��o- Stratigraphic Setting of the Ligurian Sea-Northern Apennines-Adriatic Foreland from Integrated CROP Seismic Data . In: Finetti I.R. (Ed.), Deep Seismic Exploration of the Central Mediterranean and Italy, CROP PROJECT. Elsevier, Chapter 8, 119-158. Mantovani E., Viti M., Babbucci D., Tamburelli C., Albarello D.; 2006: Geodynamic connection between the indentation of Arabia and the Neogene tectonic evolution of the central-eastern Mediterranean region, in: “Post- collisional tectonics and magmatism in the eastern Mediterranean region” . ����� �� ��� �������� �� ������ ��� Dilek Y. and Pavlides S. (Ed.), GSA special volume, 409 , 15-41. Mantovani E., Babbucci D., Tamburelli C., Viti M.; 2009: A review on the driving mechanism of the Tyrrhenian- Apennines system: implications for the present seismotectonic setting in the Central-Northern Apennines . Tectonophysics, 476 , 22-40, doi:10.1016/j.tecto.2008.10.032. Mantovani E., Viti M., Babbucci D., Albarello D., Cenni N., Vannucchi A.; 2010: Long-term earthquake triggering in the southern and Northern Apennines. �� ����������� J. Seismology, 1 4, 53-65, doi: 10.1007/s10950-008-9141-z. Mantovani E., Viti M., Babbucci D., Cenni N., Tamburelli C., Vannucchi A.; 2012: Middle term prediction of earthquakes in Italy: some remarks on empirical and deterministic approaches . ����� ������� ����� ������ Boll. Geofis. Teor. Appl., 53 , 89-111. Mantovani E., Viti M., Babbucci D., Tamburelli C., Cenni N., Baglione M., D’Intinosante V.; 2014: Generation of back-arc basins as side effect of shortening processes: examples from the Central Mediterranean . International Journal of Geosciences, 5 , in press. Mantovani E., Viti M., Babbucci D., Tamburelli C., Cenni N., Baglione M., D’Intinosante V.; 2014b: Recognition of periAdriatic seismic zones most prone to next major earthquakes: insights from a deterministic approach . In: D’Amico S. (Ed.), Earthquakes and Their Impact on Society. Springer Natural Hazard Seriee, Springer, in press. Mirabella F., Barchi M., Lupattelli A., Stucchi E., Ciaccio M.G.; 2008: �I nsights on the seismogenic layer thickness from the upper crust structure of the Umbria-Marche Apennines (central Italy) . ���������� ��� ������� Tectonics, 27, TC1010. Piccardi L, Tondi G, Cello G.; 2006: Geo-structural evidence for active oblique extension in South-Central Italy . In: Pinter, N. et al., (eds.) The Adria microplate: GPS Geodesy, Tectonics and Hazard. �������� ������� ������� Springer Verlag, 95-108. 186 GNGTS 2014 S essione 1.2