Geochemical and geomorphological analyses on liquefaction occurred during the 2012 emilia seismic sequence

Abstract

On May 20th and 29th, 2012 two earthquakes (ML 5.9 with hypocenter depth at 6.3 km and ML 5.8 with hypocenter depth at 10.2 km, respectively; ISIDe Database) struck the Emilia area. The epicentre was located in the vicinity of Finale Emilia and Medolla (Modena). Co-seismic effects exemplified by liquefactions and surface ruptures occurred in the surrounding area (Provinces of Bologna, Ferrara, Modena, Reggio Emilia, Mantova and Rovigo). The maximum effects where concentrated along the towns located 15-25 km from the epicentre (SW portion of Ferrara Province). Soon after the main events, several geochemical and geophysical surveys were carried out in different sites at Modena and Ferrara Provinces, where surface rupture and liquefaction effects were most evident. Results gained from soil and dissolved gases and geoelectrical-geophysical surveys evidenced that the main liquefied layer is related to a medium coarse-grained sand saturated aquifer located at 8-12 m b.g.l. On the other hand, superficial unsaturated sediments underwent liquefaction represented by densification and lateral spreading. As a consequence, liquefied soil caused ground failures and damages to the built environment. The extent of the liquefaction phenomena, its concentration along the Reno paleo-river ridge and the building damage, has highlighted the need to further characterized the possible rule of lithology and natural gas content on the outset of liquefaction.