The role of aftershocks in the liquefaction phenomena caused by the Emilia 2012 seismic sequence

Extensive and spectacular phenomena of soil liquefaction were observed during the Emilia seismic sequence that struck northern Italy on May-June 2012. A back-analysis with simplified procedures based on empirical correlations reveals a small liquefaction potential, which apparently underestimates the observed surface effects. Multiple and close-in-time events were a peculiar aspect of the sequence but cannot be accounted for within the simplified procedure. This study investigates their possible role in excess pore pressure build-up and hence liquefaction triggering. Results of a numerical analysis suggest that aftershocks played a determinant role, leading liquefaction phenomena to such a great extent as observed in the field. This evidence is to be considered when assessing the results obtained with empirical correlations.