Geological and geotechnical models definition for 3rd level seismic microzonation studies in Central Italy

The 2016–2017 seismic events that struck central Italy led the Government to carry out a project to produce the third level Seismic Microzonation studies in 138 municipalities. These activities have involved many experts in different disciplines such as geology, geomorphology, geophysics, seismology and geotechnical engineering. This project represented the first opportunity to perform nationally coordinated third level Seismic Microzonation studies over a wide area in a quite short time (6 months). It provided the chance to improve methodological procedures, to test the reliability of methods and models for site response analyses and to produce a huge amount of validated data. This paper focuses on the contribution of geological disciplines and concerns: (a) the definition of the main “morphostructural domains” of the Central-Northern Apennines; (b) the creation of an archive of all the lithostratigraphic units occurring in the study area with their conversion into engineering-geological units and their distribution in the different morphostructural domains; (c) the construction of the reference geological and geotechnical models, which are essential to classify the territory into seismically homogeneous microzones and to perform the successive 1D and 2D numerical analyses of the local site response. The geophysical dataset acquired for the study allowed a first statistical characterization of the Vs values typical of the engineering-geological units identified in this study. Some examples of the recurrent geological and geotechnical models are shown to explain the complexity and variety of the geological and geomorphological features of the investigated area and to highlight the different seismostratigraphic behavior of rocks and cover terrains. The analysis of third level Seismic Microzonation data made it possible to identify recurrent subsoil models and to note the main stratigraphic and morphological control-factors of the ground motion modification in the different morphostructural domains.