Historical tectonic activity along the eastern segment of the Bassano-Valdobbiadene Thrust: new hints for the seismic hazard assessment of the Venetian Prealps between Vittorio Veneto and Valdobbiadene (eastern Southern Alps, NE Italy)

Abstract. In the framework of the Italian Seismic Microzonation Project, we investigated the easternmost segment of the Bassano–Valdobbiadene Thrust Auct. (i.e. the Vittorio Veneto–Valdobbiadene Thrust) which runs at the base of the Venetian prealpine foothill between Miane, Follina and Cison di Valmarino municipalities (NE Italy). The Bassano–Valdobbiadene Thrust belongs to the SW–NE striking, SE–verging Pliocene–Quaternary front of the eastern Southern Alps which at present, accommodates deformation with velocities of the order of 2–3 mm/yr. Prominent geological and morphological expression (Mt. Grappa–Mt. Cesen–Mt. Visentin anticlines) underlies the Miocene to Present tectonic activity of the Bassano–Valdobbiadene Thrust, however the Quaternary tectonic activity is scarcely constrained. The historical seismicity reveals that few destructive earthquakes (M≥5.5) hit the Venetian prealpine region, but no significant seismic events affected Follina and the surrounding areas during the last millennium. In order to investigate the recent tectonic activity of this sector of the eastern Southalpine front, we made a morphotectonic survey along the San Pietro and Soligo valleys (i.e. the Vallata valley) and, in correspondence of possible morphotectonic evidence, a series of Electroresistivity Tomography investigations. Following, we dug some paleoseismological trenches across the possible surficial trace of the tectonic structure. The results of our study pinpointed that the Vittorio Veneto–Valdobbiadene Th. is an active fault, capable to generate linear morphogenic earthquakes. Particularly, the paleoseismological analysis highlighted that the last seismic event referable to the investigated structure occurred during the High–Middle Age (13th–14th century CE). The event produced a maximum observed displacement of 32 cm, while magnitude estimates suggest an earthquake of Mw 6.5–6.7. These data provide new important seismotectonic hints, which have to be considered in order to re–evaluate the seismic hazard of the Venetian Prealpine region, characterized by high population and industrial density.