Assessment of liquefaction potential for two liquefaction prone area considering the May 20, 2012 Emilia (Italy) earthquake

On the 20th and 29th of May 2012, two earthquakes occurred in Emilia-Romagna region (Northern Italy) triggering extensive liquefaction of the subsoil units. The consequences of liquefaction have been observed and reported by several agencies in a widespread area. The most impressive liquefaction manifestations were documented in a zone 3-4. km-long and 1. km-wide, where the villages of Sant'Agostino, San Carlo and Mirabello are located. The existing post-earthquake reports and the availability of geotechnical data provided by in-situ tests consist the basic ingredients for a computation of the liquefaction potential parameters within this zone. In particular, the Liquefaction Potential Index (LPI) and Liquefaction Severity Number (LSN) indexes were evaluated and then correlated by considering liquefaction phenomena either observed on site or not. Thus, the existing classifications of the LPI and LSN were evaluated and compared with the observed liquefaction-induced deformations. The latter was applied and validated for the first time within a liquefiable area using post-earthquake data, after the development by Tonkin and Taylor (2013). The outcome of this study shows that a threshold value of LPI around 13 or 14 is better to be taken into account instead of 5 for discriminating sites where liquefaction surface evidences should be expected from the 'non-liquefied' ones. Moreover, from the correlation of the LSN values with the cases of liquefaction-induced ground disruption it is concluded that the proposed threshold value of 10 fits statistically well with our dataset. In addition, a preliminary correlation of LPI and LSN indicates a trend that could be useful in future studies for delineating sites likely to liquefaction.