Seismic Landscape of the Monferrato Arc

The Emilia and Lombardia 2012 seismic sequence (two main shocks of Mw ca. 6.0) revamped once again the scientific debate about the seismic hazard posed by Quaternary tectonic structures of the Po Plain foredeep (e.g., Serva, 1990; Boccaletti et al., 2004; Picotti and Pazzaglia, 2008; Michetti et al., 2012; Galli et al., 2012). The W sector of the foredeep represents in particular the area with most controversial interpretation in terms of active tectonics and seismic potential. For instance, in the ITHACA catalogue of capable faults the Monferrato Arc is regarded as a seismogenic structure with potential for surface faulting earthquakes; while in the DISS database the W Lombardia and Piemonte are essentially interpreted as areas lacking any evidence of active faulting and seismic sources with Mw > 5.5. In order to attack this issue, we conducted field investigation, geomorphic analyses and the revision of the large existing database of seismic reflection profiles covering the study area in order to assess the seismic landscape of the Monferrato Arc. Our investigations confirm that the Late Quaternary landscape evolution of the South-Central Piemonte is the result of the interaction between active tectonics and widespread phenomena of river avulsion and piracy, which affected virtually the whole Piemonte and nearby Liguria region. In fact, these dramatic changes in the regional drainage network are controlled by shortening and thrust fault growth, which started during Oligo-Miocene times and is still active with visible deformation rates (Carraro et al., 1995). The development of the Apennines buried thrust fronts since Miocene give rise to the progressive uplift of the Monferrato and Torino Hills, translated above the depositional sequences of the Po Plain foredeep. The continuing deformation and displacement of the surficial deposits up to at least the Mid Pleistocene allow us to regard the buried structures of the Monferrato Arc as potentially capable faults (IAEA, 2010). Therefore, based on the available data, the regional seismotectonic framework for the W Po Plain is comparable with the one already recognized in the Emilia Arc or in the LombardiaVeneto S Alps (Modena 2012, Brescia 1222, Verona 1117). The seismic landscape of the Monferrato Arc thus includes potential surface faulting earthquakes, with M max in the order of 6.0 – 6.5 (Michetti et al., 2012), and accompanied by considerable liquefaction and earthquake environmental effects.