GNGTS 2015 - Atti del 34° Convegno Nazionale

- The longitudinal compression exerted by the Rapolano ridge, being mostly applied to the eastern sector of the Chianti ridge could be responsible for the generation of a longitudinal decoupling faults located inside that ridge, such as the SSE-NNW Montegrossi fault system (Fig. 2). The above fault may allow a sinistral sliding between the eastern and western parts of the Chianti ridge. - More to the north, the relative northward displacement of the Chianti ridge with respect to the adjacent less mobile structures (Albano ridge and Firenze-Pistoia basin) may be accommodated by a system of S-N to SW-NE faults, such as the Antella, Maiano-Bagno a Ripoli and Scandicci-Castello ones, which are probably related with the most intense historical earthquakes (1148 I VII, M 5.2; 1453 I VII-VIII, M 5.3; 1895 I VIII, M 5.4; 1959 I VII, M 4.8) that occurred in the Firenze area . - The recent seismic swarms occurred in the Elsa-Pesa and western Chianti zones (from December, 2014 until January, 2015) may have been generated by the systemof SSE-NNW to S-N faults in the Elsa-Pesa basin, which might constitute the northward prolongation of the faults located in the western side of the Chianti ridge (Fig. 2). This hypothesis is compatible with the fault plane solutions of six moderate shallow earthquakes �������� occurred during the above swarms, which coherently indicate a strike-slip strain regime, with P and T axes directed NW-SE and NE-SW respectively (data available at www.ingv. it). ����� ������ ��� �������� ������� ���� ��� ���� ������� ���������� ������������� ��� These faults are probably related with the 1812 intense earthquake (I VII-VIII, M 5.2). The proposed tectonic setting in the interaction zone between the Chianti ridge and the RMU wedge implies that the fault systems located in the Firenze area and the ones lying in the western Chianti and Elsa-Pesa zones both favour the decoupling of the Chianti ridge from the less mobile structures (Albano ridge and Pistoia-Firenze basin) lying to the west of that ridge. This means that the seismic activation of one of those fault systems may increase tectonic load (and earthquake probability) in the other zone. Such tectonic connection could explain why the seismic phases in those two zones show an interesting time correlation� ���� �������������� . This correspondence Fig. 2 – Main tectonic features recognized in the inner side of the northern Apennines (after Viti et al. , 2015). 1) Quaternary uplift 2) Deposits of travertines and calcareous tufa 3) Quaternary Umbrian volcanism 4) Faults where late Quaternary activity is likely 5) Inferred or buried faults with uncertain late Quaternary activity. Northern Lazio volcanoes (Roman magmatic body): Ci Cimini, Sb Sabatini, Vu Vulsini. Main ridges: AL Albano, CE Cetona, CH Chianti, CM Colline Metallifere, Li Livorno Mts., Pi Pisano Mt., PRM Pratomagno, RAP Rapolano, WU Western Umbria. Neogene basins: Al Albegna, Ca Casentino, Ce Cecina, Ci Cornia, Ch Chiana, El Elsa, Er Era, Gr Grosseto, LT Lower Tiber, LV Lower Valdarno, Mu Mugello, Pe Pesa, PF Pistoia-Firenze, Rc Radicondoli; Ra Radicofani, Si Siena, TF Tora-Fine, To Topino, UV Upper Valdarno, UT Upper Tiber. Fault systems: An Antella, Am Ambra (Rapale), Ar Arbia, At Amiata, Cr Ceriti, Ct Cetona, Gs Guardistallo, Lr Latera, MB Maiano-Bagno a Ripoli, Mg Montegrossi, Po Poggibonsi, Rp Rapolano, Sc Scandicci-Castello, Se Sentino, St Sarteano, Tf Tolfa. GNGTS 2015 S essione 1.2 137