Multiscale geophysical investigation on the Budoia-Aviano thrust system (NE Italy): first results

The work group is involved in the framework of the PRIN2020 research project (NASA4SHA), which aims to identify the complexity of faults in active thrust systems in Northern Apennines and Southern Alps in Italy. The paper describes the application of a multi-scale geophysical investigations applied on the Budoia-Aviano thrust system, that is part of the Polcenigo–Montereale fault system. 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). The proposed methodology included deep and shallow geoelectrical and GPR techniques to upscale the buried geological structures and to identify the site for the excavation of paleoseismological trenches. The adopted multiscale geophysical approach was applied in the studied area perpendicularly to the morphotectonic evidence of the Budoia-Aviano fault. The first step of the multiscale approach defined a Deep Electrical Resistivity Tomography (DERT). The DERT was long around 6000m, and it was able to obtain an investigation depth of about 1000m. The used DERT apparatus is a multichannel system designed and implemented by the CNR-IMAA (Rizzo et al.2004; Rizzo and Giampaolo, 2019). The acquired DERT data set was processed and elaborated through a procedure built ad hoc for this type of geoelectric surveys. While the first step highlighted the deep geological structure, several shallow high resolution geophysical surveys were planned close the morphotectonic evidence along the Budoia-Aviano thrust fault. Several shallow Electrical Resistivity Tomographies (ERT) with different electrode spacing were carried out. Three ERTs were carried out with an electrode spacing of about 5m obtaining an investigation depth of about 60m. Consequently, in order to increase the shallow resolution, a high resolution ERT with an electrode spacing of about 1m was acquired. The results of the shallow ERTs highlighted the buried geological structures in terms of subsurface faults and geological formations. Moreover, taking in account the previous results, several GPR profiles were carried out on the investigated area and the obtained results permitted to identify the site for the excavation of two paleoseismological trenches (Poli et al., at this session 1.1). The GPR results well depicted the highresolution image of the buried geological deformation, that were highlighted during the excavation phase (Poli et al., 2024). Finally, the multiscale geophysical approach allowed to improve the interpretation of previous geological and morphotectonic studies of the investigated area.