PERL: A multilevel strategy for liquefaction hazard assessment in complex stratigraphic successions

In May and June 2012, Emilia region (Italy) was struck by a seismic crisis characterized by morethan 2000 earthquakes with two main shocks (20 May and 29 May events with ML 5.9 and 5.8,respectively) and several earthquake-induced effects. Relevant liquefaction events were observedall over the area showing a maximum intensity at San Carlo and Mirabello, two main hamlets inthe Terre del Reno Municipality. In this work, a methodology is proposed for assessing liquefactionsusceptibility in wide areas characterized by complex geo-stratigraphic conditions through a multi-level approach based on simplified models. To this aim, extensive geological studies and morethan one thousand geophysical and geotechnical surveys available from previous studies havebeen collected in a dedicated geographical information system. The database is structured toguarantee data and metadata harmonization and standardization, useful for the realization of anintegrated and interoperable system progressively supplemented with new information.Preliminary 2D and 3D high resolution geological and geotechnical models are elaborated toreconstruct the complex subsoil setting of Terre del Reno area. This study forms the base for the2D numerical modelling carried out with a finite difference code (FLAC) to identify the mechanismof pore pressure increase and of liquefaction triggering. The rationale behind this study concernsthe definition of a simplified approach based on synthetic indicators. Specifically, starting fromparametric analyses, the role of different variables on the triggering process is evaluated togetherwith the definition of set of thresholds able to model the occurrence of liquefaction effects. Thespatial variability of the soil properties, layering and mechanical characteristics is considered witha geo-statistical approach. A comparison between the liquefaction effects observed in 2012 andthe results obtained from calculations is performed for demonstrating the reliability of theproposed approach in extensively simulating a liquefaction occurrence.