An integrated approach for engineering - geological modelling in view of seismic microzonation

Terre del Reno is a municipality in the Emilia-Romagna Region (Italy) that experienced relevant liquefaction events during the 2012 seismic crisis, which was characterised by two main shocks (ML 5.9 and 5.8).  Such events are mainly related to the complex geo-stratigraphic setting of the area. In this background, the present work is devoted to achieving two main objectives: i) define a new integrated methodology to assess liquefaction susceptibility in complex stratigraphic conditions through a multi-level approach; ii) perform a level 3 seismic microzonation study of Terre del Reno. To this purpose, more than one thousand geophysical and geotechnical measurements available from three different databases and some hundreds of new collected investigations were stored in a dedicated geodatabase. Data and metadata, that were spatially and statistically manipulated to guarantee their harmonization, standardization, and uniqueness, were explored to reconstruct a model for the Terre del Reno subsoil. Specifically, a geological model of the studied area (~ several hundreds of meters) was first reconstructed as well as the seismic bedrock geometry (the latter defines as the layer characterized by the stiffness requirement: Vs > 800 m/s). This model was obtained by integrating deep bore-hole data available from previous studies and geophysical and geotechnical investigations. Furthermore, a high-resolution geological reconstruction of the upper 30 m has also been performed through sedimentological and paleo morphological analysis to characterize the sedimentary units affected by liquefaction. This analysis may be used to compare both well-known and innovative geotechnical indicators for liquefaction susceptibility assessment. Thus, a set of acceleration time histories, that are spectrum-compatibles with the spectrum of reference input motion at outcropping bedrock of the site, were used as input in 1D and 2D site effect numerical modelling. The obtained results were synthetized and represented in a level 3 seismic microzonation study with the aim of providing operational indicators devoted to urban planning and for challenging problem related to liquefaction.