Role of the long-lived Schio-Vicenza Fault System at the northern Adria plate margin

Abstract

We present a review of geological and seismological data on the long-lived Schio-Vicenza Fault System (SVFS) at the northern Adria plate margin and provide its geodynamic and seismotectonic interpretation. The SVFS is a NW-SE trending, high angle complex structure transverse to the Southern Alps fold-and-thrust belt, and has been the object of geological and structural studies for more than a century and a half. The main segment of the SVFS is the Schio-Vicenza Fault (SVF), which has a significant imprint in the landscape across the Eastern Southern Alps and the Veneto-Friuli foreland. The SVFS is divided into a northern segment, extending across the chain between the town of Schio and the Adige Valley, and a southern one, coinciding with the SVF proper. The SVF borders to the east a foreland structural and morphological high formed by the Lessini and Berici Mts., where the Mesozoic bedrock is exposed, and by the volcanic Euganei Hills, separating it from the Veneto-Friuli foreland, and continuing southeastward up to the Adriatic coastline along the blind Conselve-Pomposa Fault. The segments of the SVFS have been active during several tectonic phases with different styles of faulting at least since the Mesozoic, with a well defined long-term dip-slip component of faulting and, conversely, a horizontal one not well constrained. The SVFS interrupts the continuity of the Southern Alps thrust fronts in the Veneto sector, suggesting that at least it played a passive role in controlling the geometry of the active thrust belt, and possibly also the current distribution of seismic release. In this context, the SVFS, and specifically its SVF segment, has been interpreted as the sinistral strike-slip boundary of the northeastern Adriatic indenter. The recent activity of the SVFS is highlighted by the moderate seismicity along the northern segment and few geological observations along the southern one. The review of the historical and instrumental seismicity along with active deformation data, shows that the SVFS does not appear to have generated large earthquakes during the last few hundred years, while the focal mechanisms of moderate seismicity points to a dextral strike-slip activity, driven by a N-S oriented compressional regime. These observations are corroborated by the field analysis of antithetic Riedel structures of the fault cropping out along the northern segment. Conversely, the southern segment shows geological evidence of recent sinistral strike-slip activity. The geological and seismological apparently conflicting data can be reconciled considering the sinistral strike-slip faulting style of the southern segment as driven by the indentation of the Adriatic plate, while the dextral strike-slip style along the northern segment can be explained as a sinistral opening "zipper" type shear zone junction, where intersecting pairs of simultaneously active faults with different sense of shear merge into a single fault system through a zippered section.