GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 109 In this northernmost sector of the inner Apennines, extensional fault activity followed, and possibly accompanied, the Apuan Alps exhumation to the south since early Pliocene. Despite some peculiar characteristics, the Quaternary sediments of the Lunigiana and Garfagnana basins describe a common general evolution. The basins are filled with continental deposits that generally show an evolution from low-energy fluvial environment, lake and marsh (lower Pliocene-lower Pleistocene) to coarse-grained fluvial deposits (lower Pleistocene) and finally alluvial deposits organized in terraces and fans (middle Pleistocene-Holocene) (Federici, 1978; Puccinelli, 1987; Bernini et al. , 1991; Bertoldi, 1997; Bernini and Papani, 2002; Landi et al. , 2003; Perilli et al. , 2004; Coltorti et al. , 2008). Historical and recent seismicity (i.e. the 2013, June 21, Mw 5.1 event) confirm that the transfer zone between Lunigiana and Garfagnana graben is seismically active and is considered the most hazardous area of the Northern Apennines (Pezzo et al., 2014). Moreover, the actual seismic hazard posed by the Lunigiana rather long fault systems (> 30 km) is not completely resolved, especially for the lack of field data focused on the characterization of fault capability. This note is a first contribution to fill this knowledge gap for the southwestern fault-bound edge of the Lunigiana: the Mulazzo Fault. As a contribution to the project on active faults prompted by the Tuscany Region, a detailed structural and geological investigation was carried out across the whole Lunigiana basin (covering an area of about 1000 km 2 ), resulting in a new map of the active tectonic structures in the area (Fig. 1a). Moreover, along the most prominent fault systems a geomorphic analysis was performed with the aim to estimate their cumulative throw and variations along strike, the segmentation pattern within each system and any possible interaction between faults. Footwall relief was measured through the topographic analysis of 44 swath profiles built on 5x5 DEM along the Mulazzo (MUL, 34 km long) and the Coloretta-Montereggio-Aulla (CMA, 22 km long) systems on the western border of the basin and along the Groppodalosio-Compione-Comano (GCC, 38 km long) on the eastern border. The cumulative throw and footwall profiles along fault strike were compared with prominent knickpoints detected along river profiles crossing the fault systems. Knickpoint heights scale with footwall relief and documented fault throw. Fig. 1 - Left: A) Tectonic sketch-map of the Lunigiana basin. Main fault systems and the site of the paleoseismic trench across the Mulazzo fault are marked. Right: B) geological map of the central sector of the Mulazzo fault wrapped on LiDAR bare-earth image. MAC: Macigno Formation, upper Oligocene-early Miocene; OLP: Olivola conglomerate, lower Pleistocene; b: alluvial deposits, ?upper Pleistocene-?Holocene. C) Topographic cross section across the fault scarp of the Mulazzo fault; the location of the paleoseismic trench is shown.