Three-dimensional geological modelling of the western sector of the Po Plain (Italy) for seismic site response evaluation

It is widely recognized that a significant part of the variability of earthquake ground motion is related to local geological conditions, which can strongly modify the ground-motion amplitude, duration and frequency. This is commonly referred to as seismic response of a site. In the case of sedimentary basins, the characteristics of the soil deposits and the buried geometry of the basin can strongly influence the nature of the surface shaking, which may be amplified or reduced. Therefore, the knowledge of the 3D structure of the subsoil is crucial for seismic hazard studies and seismic risk management. 

To this end, 3D geological modeling allows the combination of multidisciplinary data in the shaping and visualization of the current knowledge of the subsoil and allows integration with new data or interpretations, as they become available (Calcagno, 2015). Moreover, 3D geological models represent the basis for physics-based numerical simulations, provided that a reliable scientific procedure is defined to convert the different types and levels of the available complex geological information (Klin et a., 2019).

The aim of this study is to create a 3D seismo-stratigraphic model of the central-western portion of the Po Plain, one of the deepest and widest sedimentary basins worldwide that can reach about 8 km in the Apennine foredeep (Pieri and Groppi, 1981). Although its topography is mostly flat, the buried geometry is quite complex, with north-verging thrust systems of the Apennines and south-verging thrust systems of the Alps. The 3D geological model was implemented through the integration of geological cross sections (Pieri and Groppi 1981, Casero 2004, Fantoni and Franciosi 2010, Maesano et al., 2015), deep drill holes (VIDEPI project) and geophysical surveys (sonic logs, microtremor single-station and array measurements; MASW and downhole surveys). We relied on the commercial GeoModeller software by Intrepid Geophysics for merging and interpolating the geological and geophysical data to create a 3D digital model, that is initially used to simulate 1D wave propagation and represents the basis for further improvements and 2D / 3D modelling.