GNGTS 2015 - Atti del 34° Convegno Nazionale

seismic sources (Norcia-Colfiorito-Gualdo Tadino-Gubbio-Upper Tiber, Mugello, Garfagnana and Lunigiana) are located in the zones where adjacent ridges have undergone different oroclinal bendings, inducing transtensional deformation. The fact that the effects of the above shortening processes have progressively involved more and more outer sectors of the northern Apennines is closely connected with the activation of more and more eastern decoupling fault systems (Latina, Val Roveto, Fucino and L’Aquila) in the Lazio-Abruzzi indenter (Fig. 1). The recent (late Pleistocene) development of the L’Aquila fault, in the inner side of the Gran Sasso arc, has favoured the formation of a major discontinuity in the northern Apennines (Norcia-Colfiorito- Gualdo Tadino-Gubbio), whose seismic activations allow the transtensional decoupling of the outermost sector of the RMU wedge from the inner belt (Fig. 1d). Sometimes, this decoupling extends northward, through the Upper Tiber and Romagna-Forlì fault systems. Belt-parallel compression has also stressed the ����� ���� �� ��� �������� ���������� ���� inner side of the northern Apennines, even though at a lower rate. Such process ��� ������ ������������ ���������� ��� ������ �� ��� ����� ��� has caused longitudinal shortening and uplift of the ridge and basin systems that had formed during the upper Miocene and early Pliocene. The most evident effects of this deformation can be recognized in the Albano-Chianti-Rapolano-Cetona ridge and surrounding basins. The proposed tectonic context could explain why the Upper Valdarno and Chiana basins, lying along the outer boundary of that ridge, are almost aseismic, whereas the Elsa, Pesa, Siena and Radicofani basins, lying at the inner side of the same ridge, are affected by moderate seismic activity. The interaction between the Chianti-Rapolano-Cetona ridge and the northern part of the RMU wedge has generated seismogenic fault systems in the Firenze area. The correlation tentatively recognized between the time patterns of seismic activity in that zone and in western Chianti could be related with the fact that the activations of those fault systems both favour the decoupling of the Chianti ridge from the surrounding structures. Finally, the long-termkinematic pattern deduced by theQuaternary deformation is compatible with the present velocity field indicated by space geodetic measurements. In particular, the above observations, being provided by a fairly dense network of continuous GPS sites, allow us to propose a good definition of the Apennine sectors which are characterized by different kinematic regimes. References Acocella V., Funiciello R.; 2006: Transverse systems along the extensional Tyrrhenian margin of Central Italy and their influence on volcanism. Tectonics, 25 , TC2003. Bosellini A.: 2004: The Western passive margin of Adria and its carbonate platforms . Special volume of the Italian Geological Society for the 32 nd International Geological Congress, Florence, Italy, 79-92. 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. Ciarapica G., Passeri L.; 2005: Late Triassic and Early Jurassic sedimentary evolution of the Northern Apennines: an overview. ����� ���� ����� ���� Boll. Soc. Geol. It., 124 , 189-201. Gudmundsson A.; 2001: Fluid overpressure and flow in fault zones: field measurements and models. Tectonophysics, 336 , 183-197. 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. (Eds.), Geol. Soc. Am., 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: jmplications for the present seismotectonic setting in the Central-Northern Apennines . Tectonophysics, 476 , 22-40. 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, 14 , 53-65. 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. GNGTS 2015 S essione 1.2 139