GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 Conclusions By further using the physically based modelling of 3D seismic wave propagation in the Arquata del Tronto area, produced by Primofiore et al. (2020), we hoped to provide some general results related to induced site effects. By comparing 2D and 3D analyses, we recognize large differences, both in amplification values and in corresponding frequencies. In Borgo area, although there are different amplitudes between 2D and 3D, the peak values are at the same frequencies. These differences are related to both constitutive laws and geomorphological features. Nevertheless, the contribution of each factor cannot be separated. In the 3D model, the linear viscoelastic behavior, meaning that a constant damping is assumed, generates greater amplification than the equivalent linear constitutive law of the 2D model. At the same time, the 3D geometry considers deformations in the whole volume despite the 2D geometry , which does not assume deformations outside the model plane. Therefore, the results of the different assumptions cannot be predicted separately. However, our interest is focused on the spatial distribution of the amplified frequencies. The 3D simulations allow the authors to capture broadband amplified frequencies on the Arquata hill, where the 2D simulations fail. Two important aggravation factors, that are not captured by 2D analyses, can be recognised: (1) the polarisation of the oscillation as a function of the directions of the input seismic waves; (2) the torsional deformation induced by geomorphological irregularities, the slope, and the Vs spatial distribution on asymmetric ridges, such as Arquata del Tronto hill. Thus, 3D simulations should be preferred to predict the local seismic effects in such a case. Acknowledgment This study has been developed within the agreement for the seismic microzonation studies in Central Italy between University “G. D’Annunzio” of Chieti-Pescara and the Institute of the environmental geology and engineering geology of the Council of National Research (CNR - IGAG) (Prot. 0002282 del 27/7/2017). References Baron J., Primofiore I., Klin P., Vessia G. and Laurenzano G.; 2022: Investigation of topographic site effects using 3D waveform modelling: amplification, polarization and torsional motions in the case study of Arquata del Tronto (Italy). Bull Earthquake Eng 20, 677–710. https://doi.org/10.1007/s10518-021-01270-2