GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Recent actvity of the Stradella fault (Emilia Arc, northern Italy) by a mult-scale approach A. Tibaldi 1,2 , R. de Nardis 3,2 , P. Torrese 4,2 , S. Bressan 1 , M. Pedicini 1 , D. Talone 2,3 , F. L. Bonali 1,2 , N. Cort 1 , E. Russo 1,2 , G. Lavecchia 3,2 1 Department of Earth and Environmental Sciences, University of Milan-Bicocca, Milan, Italy 2 CRUST-Interuniversity Center for 3D Seismotectonics with Territorial Applicatons, Chiet, Italy 3 Department of Psychological Sciences, Health and Territory, University of the Studies “G. d’Annunzio”, Chiet, Italy 4 Department of Earth and Environmental Sciences, University of Pavia, Italy The deformaton front of the northern Apennines - Italy - is mostly covered under the alluvial deposits of the Po Plain. Some of the folds and thrusts of this front show geological evidence of Late Quaternary actvity, thus posing the need for an accurate seismic hazard assessment due to widespread housing setlements, industries, lifeline infrastructures, and large towns. We present new morphostructural, geophysical, and seismological data to discuss the recent actvity of the Broni-Sarmato fault, an 18 km-long outcropping secton of the north-verging Stradella thrust, located 50 km south of Milan, along the Pede-Apennine thrust front (PTF) in the rear of the Emilia Arc thrust system. The new geoelectrical surveys across the fault scarp show deformaton of the shallow deposits. The outcropping deformatons, with a fault scarp ranging up to 25.8 m, are investgated within the seismotectonic framework of the PTF and the Emilia Arc. The analysis of the associated seismicity and new focal mechanisms highlight two seismogenic contractonal volumes dipping at low-angle southwest-ward, at upper (<12 km) and lower crustal depths (~20– 30 km). The shallow seismicity partally illuminates the Stradella thrust and its alongstrike southeastward prosecuton along the extent of the Stradella-Salsomaggiore Arc. Subordinately, it also illuminates some of the Emilia Arc thrust planes. The deeper seismogenic volume shows large patches of the basal thrust of the Emilia Arc fault system. We interpret the above mult-scale data as evidence of ongoing tectonic actvity of the outer fronts of the Emilia Arc under a regional NNE- oriented compressional stress feld, with some evidence of thrust involvement along the Pede- Apennine front. In our 3D fault-model reconstructon, all the analyzed thrust structures appear as expressions of a thick-skinned deformaton that controls earthquake release at diferent structural levels. The results do not allow to establish if the Broni-Sarmato scarp really represents the emersion of the main fault or it can represent the frontal limb of a fault-propagaton fold. In the later case, the main thrust did not reach yet the surface, whereas the deformatons of the shallow deposits, highlighted by geoelectrical surveys, may represent secondary structures.