New palaeoseismological evidence of coseismic surface rupture across the Carnic Prealpine front (NE Italy): the Budoia-Aviano Thrust System

In the framework of the PRIN_2020 “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy (NASA4SHA)”, we conducted a palaeoseismological study into the area comprised between the Budoia and Aviano localities (western Carnic Prealps, NE Italy). The investigated area, which is part of the external Plio-Quaternary front of the Eastern Southalpine Chain, is characterized by the presence of distinct WSW-ENE trending and S-verging reverse fault planes arranged in thrust systems and affecting the Quaternary succession (Poli et al., 2014). In detail, the geological and morphotectonic survey highlighted many evidence of recent deformation affecting the Last Glacial Maximum alluvial fan of the Artugna Stream, including morphological anomalies of both the topography (scarps) and the hydrography of minor streams. Following the multidisciplinary and multiscale approach, the preliminary geophysical survey, which included multiscale Electric Resistivity Tomograhy (DERT and ERT) and Ground Penetrating Radar (GPR), allowed us to identify the site for the excavation of two palaeoseismological trenches (Rizzo et al., this session) The excavated walls intersected a set of medium-to-high angle reverse planes verging towards the North, which displace the alluvial fan stratigraphy and also affect the soil. At about 2 m depth from topography, we identified a paleosoil dividing two alluvial fan units and affected by deformation. The radiocarbon dating of the paleosoil sample revealed an age of about 16 ky BC. The palaeoseismological analysis allowed us to estimate a cumulative slip, measured on all fault planes, of the order of at least 4.5 m. Moreover, we detected at least three seismic events, the most recent of which is possibly referable to the 1873 M 6.3 Alpago - Cansiglio earthquake (CPTI15, Rovida et al., 2022). The reverse fault planes identified within the two excavated trenches define an about 20 m wide area of surficial deformation, developed at the hanging-wall of the main S-verging thrust plane and characterized by an ENE-WSW trending. If considering the lateral extension of this deformation area, it clearly affects industrial complexes, urban centres and sensitive structures of Budoia and Aviano localities. Therefore, the paleoseismological evidence collected so far provide implication which are relevant for the seismic hazard estimation of the area, and which must be necessarily considered in the framework of the regional planning.