The role of geomorphology in seismic hazard assessment: lessons from the 2012 seismic sequence in the central-southern Po Plain (northern Italy)

Since mid-May 2012, a seismic sequence affected the central-southern sector of the Po Plain (northern Italy). The drainage network evolution shows the northward migration of the River Po and the deflections of the Apennine rivers, which were explained with the uplift of the Ferrara Folds. The most relevant effect caused by the two strongest 2012 earthquakes was the 10-15 cm uplift of the epicentral area, detected by InSAR interferometry, corresponding to the hanging wall anticline of the Ferrara Folds thrusts. Therefore, similar coseismic uplifts may be responsible of the shifting of rivers Po, Secchia, Panaro and Reno in previous periods. At a detailed scale several hundreds of earthquake-induced environmental effects (EEE), mainly of the geological/geomorphological type, scattered all over the epicentral area, were detected. They were mainly represented by widespread soil liquefaction phenomena and ground ruptures, accompanied also by sand boils. The coseismic effects appeared to be concentrated along alignments which can be followed even for kilometres and be linked not only to the local stratigraphic characteristics but also to the network of abandoned riverbeds. It can be stated that EEE highlighted the importance of geomorphology for seismic hazard assessment of alluvial plain areas. Therefore, after the 2012 quakes, the location of EEE and the geomorphological features have been taken into account, beside the lithological features of the subsoil, for the implementation of seismic susceptibility maps for territorial planning in the municipalities of the epicentral area. As concerns seismic hazard perception, the tragic experiences of the 2012 earthquake-struck population, have induced some people to pay particular attention to natural phenomena appearing even one year later (gas emissions, bubbling water and ground fractures), wrongly linking them to premonitory signs of earthquakes. This fact confirms that the analysis of the geomorphological setting and of the evolution of the drainage network is a powerful tool for the identification of the activity and the seismic hazard related to buried geological structures in alluvial plains.