Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

478 PATA Days 2024 D I S C U S S I O N The small surfaces located along the eastern side of the Anghiari ridge are dipping towards NE, with a slope comparable to the gullies which incise them. This suggests that these surfaces could be related to an original surface, later displaced by the Anghiari fault, which was originally formed by the SW-NE oriented drainage, similar to the present-day drainage of the ridge towards the Tiber River, which was emplaced during the uplift of the Anghiari ridge. These surfaces have thus been probably flattened simultaneously, being part of a single cut-terrace, then incised and disjoined by the gullies and the fault activity. The area, investigated with quantitative analysis and cosmogenic nuclides dating, corresponds to the area of maximum displacement of the Anghiari fault according to the amount of along-strike exhumation of the ridge. The cosmogenic nuclides dating provides an exposure age of the paleosurfaces located on the eastern side of the Anghiari ridge of 45 kyr at the Cicogna 2 sites and 40-45kyr at the Villa Sterpeto site. Disregarding the uncertainties, these two ages are quite coherent with each other, confirming the hypothesis about the common origin of the surfaces and allowing to use them as a marker for the displacement and slip rate evaluation. Considering a vertical displacement of the paleosurface of 23-43 m along the Micciano fault section, the throw rate of the Micciano fault section over the last 40-45 kyr is 0.5-1.1 mm/yr. Considering a mean fault inclination of 50° (Testa et al., 2023), the slip rate corresponds to 0.6-1.3 mm/yr. This slip rate is much higher than the slip rate given by the paleoseismological investigations over the last 25kyr (0.1-0.3 mm/yr). This can be related to various aspects: i) the uncertainties in the exposure age are high and thus, the slip-rate derived over the last 45 kyr could be overestimated; ii) since the time spans are different, it is also possible that those two values reflect the different rates of activity of the fault. If that’s the case, then our results would suggest that there could have been a slow-down of the fault activity over the last 25 kyr. This hypothesis is also supported by the results of the paleoseismological data discussed in Testa et al., 2023, who suggest that the Anghiari fault seismic history can be affected by earthquake clustering alternating with longer recurrence time. C O N C L U S I O N S The qualitative and quantitative morphological analyses show that the well-preservedAnghiari ridge top paleosurface is due to a Paleo Tiber River drainage and corresponds to the top of the depositional sequence. This surface has a different origin with respect to the paleosurfaces located at different elevation along the eastern side of the Anghiari ridge. These latter, which are confirmed to be erosional surfaces, are more coherent with an SW-NE directed flow set up at the beginning of the Anghiari ridge exhumation due to the fault activity. The performed cosmogenic nuclides dating provides an age of the paleosurfaces of 40-45kyr at both the hanging-wall and footwall of the Micciano fault section. Since the ages are coherent, it is reasonable to confirm that these paleosurfaces originally belonged to the same terrace which was subsequently displaced by the fault activity. Along the Micciano fault section, the vertical displacement between the paleosurfaces ranges from 23 to 43 meters, while along a secondary splay of the Anghiari-Motina fault section, it ranges from 18 to 20 meters. The slip-rate over the last 40-45 kyr along the Micciano fault section corresponds to 0.6-1.3 mm/yr, which is significantly higher than the slip rates provided by the paleoseismology (0.1- 0.3 mm/yr). This can be related to an irregular seismic behavior of the Anghiari fault involving alternance of earthquake clustering and longer recurrence time or a slow-down of the fault activity over the last 25 kyr, or both. Quantitative geomorphology has proven to be an excellent tool to investigate active faults, particularly to find morphological markers and evaluate the along- strike long-term displacement. At the same time, cosmogenic nuclides dating constitute a valuable tool in determining the exposure age of morphological features and consequently estimating the fault slip rate. A C K N O W L E D G E M E N T S This work has been funded by the ANR Project "EQtime” (Lucilla Benedetti - CEREGE, Aix-en- Provence, France) an "Ente Acque Umbre Toscane" (EAUT - Arezzo, Italy), within a convention a with University of Chieti (Paolo Boncio) and University of Perugia (Francesco Mirabella).