First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses

Abstract

We present the findings of a multimethodological study made on the Budoia-Aviano Thrust System conducted as part of the NASA4SHA PRIN Project “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy”.The NW dipping, SW-NE striking Budoia-Aviano Thrust System represents the southeast-verging external front of the Plio-Quaternary Eastern Southalpine Chain, occurring at the front of the western Carnic Pre-Alps, between Polcenigo and Montereale (PN).The recent activity of the Budoia-Aviano thrust is evidenced by numerous geological and morphostructural features, including the exposure of Mio-Pliocene reliefs emerging from the Last Glacial Maximum alluvial plain, the upwarping of the LGM fan of the Artugna stream, and geomorphic anomalies of the surface hydrographic network (Poli et al., 2014).Moreover, to identify sites to perform excavation aimed at exploring the Holocene movements of the thrust system, we performed multiscale geophysical investigations, such as Deep Electric Resistivity Tomography, Electric Resistivity Tomography and Ground Penetrating Radar across the entire thrust system. They revealed the presence of a series of possible north-verging shear planes, whose trace seemed to correspond to the more pronounced up-ward convex profile of the Artugna alluvial fan.Based on geophysical results, two NNW-SSE paleoseismological trenches were excavated along selected GPR profiles. The trenches exposed late LGM-to-Holocene alluvial fan deposition of the Artugna stream. Notably, a paleosoil embedded in alluvial sequence yielded a 14C age interval between 16 Ky and 5 ky BCE.In both trenches, the entire excavated late Quaternary succession was affected by a set of north-verging reverse planes, coinciding with the discontinuities identified in GPR profiles. In each trench, the total vertical displacement measured across all thrust planes is of about 4.5 meters, resulting from at least three displacement events occurred in the last 7,000 years. Moreover, the involvement of the bottom of the ploughed soil supports the hypothesis of the backthrust being activated during the MW 6.3 Alpago-Cansiglio earthquake (Rovida et al., 2022) as suggested by Galadini et al. (2005).The integration of paleoseismology, photogrammetry, and high-resolution geophysics enabled the construction of a detailed 3D model of the Budoia-Aviano Thrust System, revealing a 20-meter-wide deformation zone on the hanging wall of the main south-verging Budoia-Aviano Thrust. In the perspective of seismic hazard assessment and regional planning, it is worth to consider the proximity of this active and capable fault to industrial complexes, urban centres, and vulnerable structures characterizing the Budoia and Aviano area.REFERENCESGaladini, M.E. Poli, Zanferrari, A. (2005). Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy). Geophysical Journal International, 161(3). M.E. Poli, G. Monegato, A. Zanferrari, E. Falcucci, A. Marchesini, S. Grimaz, P. Malisan, E. Del Pin (2014). Seismotectonic characterization of the western Carnic pre-alpine area between Caneva and Meduno (Ne Italy, Friuli). DPC-INGV-S1 Project. Rovida, M. Locati, R. Camassi, B. Lolli, P. Gasperini, A. Antonucci (2022). Catalogo Parametrico dei Terremoti Italiani (CPTI15), versione 4.0. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/CPTI/CPTI15.4