GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 New insights into the seismogenic potental of a low-strain rate region: actve faultng in the Siena basin (Cava Capanni quarry, Tuscany) Andrea Brogi 1,2 , Paola Vannoli 3 , Martna Zucchi 1 , Pierfrancesco Burrato 3 , Umberto Fracassi 3 , Gianluca Valensise 3 , Hsun-Ming Hu 4,5 , Chuan-Chou Shen 4,5 1 Department of Earth and Geoenvironmental Sciences (University of Bari, Italy) 2 CNR-IGG, Insttute for Geosciences and Georesources (C.N.R., Italy) 3 Isttuto Nazionale di Geofsica e Vulcanologia (Italy) 4 High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, (Natonal Taiwan University, Taiwan, ROC) 5 Research Center for Future Earth (Natonal Taiwan University, Taiwan, ROC) We investgate the actve tectonics and earthquake potental of a system of actve faults located along the eastern Siena Basin, a slowly deforming porton of southern Tuscany falling within the inner Northern Apennines. This region, although classifed as a low hazard area (Stucchi et al., 2011; Melet et al., 2021), has been frequently hit by low magnitude seismic sequences occurring in the uppermost 10 km of the crust, and ofen concentrated in clusters that appear unrelated to major known seismogenic zones, but also, by rare damaging earthquakes in the Mw range 5.0-6.0. The historical earthquake record includes events such as the 7 August 1414, Mw 5.7, Colline Metallifere; the 13 April 1558, Mw 6.0, Valdarno superiore and the 25 August 1909, Mw 5.3, Crete Senesi, earthquakes (Rovida et al., 2022). As of today, very litle is known concerning the geometry of their causatve faults, the maximum earthquake potental of such faults and their kinematc characteristcs. The Siena Basin is a Neogene structural depression that developed during the extensional evoluton of the inner Northern Apennines along NNW- to NW-striking Plio-Quaternary normal faults, and is flled by an up to 600 m thick sequence of marine terrigenous and contnental deposits (e.g. Martni et al., 2021). Diferent N-, NE- and WNW-striking fault systems actve in Zanclean-latest Quaternary tmes were described in the eastern Siena Basin (Brogi, 2004; Bambini et al., 2010; Ghinassi et al., 2021). The N-striking faults are Pliocene in age and are associated with the latest evoluton of the Siena Basin (Brogi, 2011), whereas the youngest, WNW- and NE-striking faults are Neogene-latest Quaternary in age and appear to control the locaton of thermal springs and the resultng patern of travertne depositon. The WNW-striking faults are the youngest structures and stll control the ascent of thermal water, gas emissions, and travertne depositon in some areas (e.g., Minissale et al., 2002; Minissale, 2004; Brogi and Capezzuoli, 2009; Bambini et al., 2010). These deposits are especially