GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 outcropping bedrock and flat surface topography). The main goal of this study is to propose new soil factors for NTC18 using strong motion data from an accelerometric dataset of real recordings. The work also aims at assessing the role of soil nonlinearity which is linked to both soil type (i.e., soil category) and severity of ground shaking. The activities were carried out according to the conceptual framework reported in Figure 1 and Figure 2 . A large number of weak and strong ground motion recordings have been selected from three well-known freely available strong-motion datasets: the European accelerometric archive ESM, the Japanese Kik-net and the North-American PEER-NGA. The composite accelerometric dataset includes recordings that have been simultaneously registered by pairs of seismic stations located on outcropping bedrock (i.e., V S30 > 800 m/s) and ground surface (i.e., V S30 < 800 m/s). Soil factors have been estimated using different approaches in a tentative way to address the epistemic uncertainty. The proposed new soil factors have been compared with the results obtained from a multi-parametric numerical study conducted by Andreotti et al . (2018). METHODOLOGY A metadata set representing pairs of seismic stations that simultaneously recorded the ground motion under outcropping bedrock conditions and at the ground surface was defined from the composite archive involving ESM, Kik-Net and PEER-NGA accelerometric data. The recording stations have been classified according to the current Italian building code (NTC18 Tab 3.2.II ). To remove the bias due to the different distance of each station pair, the recordings have been scaled using a ground motion model (GMM) appropriately selected for this purpose. The recording station used as reference is the one classified as belonging to a soil category other than A (i.e., with V S,eq < 800 m/s). The GMM of Bindi et al . (2014) was used for the ESM dataset, the one of Cauzzi et al . (2014) was used for the Kik-Net dataset, and the one of Boore and Atkinson (2008) was used for the NGA dataset. Finally, soil factors were defined using the geometrical mean of two horizontal