Paleo-Seismicity in the Euganean Hills Province (Northeast Italy): Constraints From Geomechanical and Geophysical Tests in the Schio-Vicenza Fault Area

Silvana Martin,Fabio Fedrizzi,Sandro Rossato,Nicola Cenni,Claudia Agnini,Giampaolo Cortellazzo,Jacopo Boaga

doi:10.3389/feart.2020.586897

Abstract

Gouges and cataclasites within exhumed fault zones are valuable indicators of past seismic events. Gouge layers, 40- to 100-cm-thick and decameters long, have been found within uplifted Cretaceous limestones in the Euganean Hills (SW of Padova, NE Italy), Cenozoic subvolcanic chambers intruded within a Meso-Cenozoic sequence. The main tectonic lineament in the area is the Schio-Vicenza Fault that bounds the Euganean Hills to the East. Micropaleontological analyses reveal that the gouges derive from the fragmentation and pulverization of the adjacent pristine carbonatic rocks. Stress tests on specimens from bedrock associated with gouges yielded a minimum dissipated strain energy of 0.3–0.5 MJ/m3to shatter them. Henceforth, additional strain energy was necessary to pulverize these rocks within the gouge zones. Global navigation satellite system observations show that the present deformation pattern in this region of Italy is a few tens of nanostrain (10–30 1/y), not enough to generate such gouge layers. Therefore, the seismicity of the Euganean Hills (currently M ≤5) must be reconsidered in the light of the Schio-Vicenza Fault past activity. The gouges may imply that the Schio-Vicenza Fault had a more intense activity in the past, or this area was affected by remote events or tectonic structures. This article provides new clues on the evolution of the tectonic and morphological setting of the area, with relevant consequences on seismic risk assessment of the nearby urbanized area, including the cities of Padova and Vicenza.

Highlights

A territory hit by earthquakes generally exhibits distinctive landforms such as compressional and extensional features, ridges, shear planes with displacement, scarps, trenches and fragmented rocks, and gouges within bedrock (i.e., Guerrieri et al, 2010; Michetti et al, 2012; Livio et al, 2014)
Before the recognition of paleo-seismic landforms indicative of earthquakes in the Southern Alps, it was generally accepted that no high-intensity seismic events, Paleo-Seismicity in the Euganean Hills with exception of the well-known earthquake of Verona in 1117, occurred in this area in the last millennia and many of the Middle Age city destructions in the NE Italy were attributed to this event (Guidoboni et al, 2005; Rovida et al, 2016)
In the area between Bassano and Pordenone, Miocene–Pliocene sequences have been deformed and uplifted in Pleistocene–Late Holocene due to the thrust activity of the Venetian-Friulian belt which was struck by earthquakes with magnitude M >5 (Galadini et al, 2005; Burrato et al, 2008; Fontana et al, 2010; Rovida et al, 2020)

Summary

Introduction

A territory hit by earthquakes generally exhibits distinctive landforms such as compressional and extensional features, ridges, shear planes with displacement, scarps, trenches and fragmented rocks, and gouges (powdered layers and pockets) within bedrock (i.e., Guerrieri et al, 2010; Michetti et al, 2012; Livio et al, 2014). These features have been observed in the central sector of the Italian Southern Alps (Vannoli et al, 2015). In the Po Plain, active blind thrusts and related transfer faults are present, and some of these are thought to act as potential triggers (i.e., Burrato et al, 2008; Vannoli et al, 2015)

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