On the Influence of Shallow Underground Structures in the Evaluation of the Seismic Signals

The evaluation of the correct seismic input represents one of the most important parameters for the design of structures, especially for those located in high seismicity areas. During last decades, several researchers have proposed different methods to obtain the seismic inputs considering also the large number of signals registration present within the different international databases. Despite these developments, some issues are still open, especially in presence of particular soil stratigraphy where the local seismic response analysis is required. Another important aspect that influence the seismic input evaluate at ground level is the presence of shallow underground structures, which change the signal trend on the surface. The paper presents the results of a sensitivity analysis referred to a shallow metro station embedded in granular soil. In particular, four different soil profiles, characterized by different value of shear waves velocity, and five acceleration time histories, recorded during European seismic events, are considered, in order to obtain the amplification coefficients of the seismic signals evaluated on surface and due to the presence of the metro station.