Geochemical and Geomorphological Analyses on Liquefaction Occurred During the 2012 Emilia Seismic Sequence

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.