Spatial variability of the urban ground motion in a highly heterogeneous site-city configurations
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Spatial variability of the urban ground motion in a highly heterogeneous site‑city configurations C. Varone1 · L. Lenti2,5 · S. Martino3 · J. F. Semblat4 Received: 6 March 2020 / Accepted: 18 September 2020 © Springer Nature B.V. 2020
Abstract Free-field conditions on the ground surface are widely used to assess the local seismic response. Nevertheless, this assumption is a very strong approximation in urban areas since the dynamic interaction between the urban agglomerate and the soil cannot be neglected. Several studies evidenced the transmission of vibrations from the buildings to the soil and the multiple interactions between a building network and the site through so-called SiteCity Interaction (SCI). This paper focuses on the spatial variability of the seismic ground motion due to SCI in the case of highly heterogeneous site-city configurations. The Fosso di Vallerano valley in Rome (Italy) has been chosen as a case study because of the high heterogeneity of the deposits which characterize the local geological setting as well as the intensive urbanization. A proper 2D numerical modelling (Finite Elements Method) of the seismic response in free-field conditions as well as with the city agglomerates (SCI-based condition) has been performed. The numerical results show a strong spatial variability of the wave field induced by the presence of the buildings and their interaction with the heterogeneous soil. The SCI effect causes a strong or global reduction of ground motion, amplification levels and kinetic energy close to the buildings. Induced perturbations affect the ground motion along the surface of the model, increasing the amplification values and the kinetic energy in the vicinity of the buildings. These findings highlight that buildings generate significant variability effects all around their foundations as well as in the entire alluvial basin. Keywords Wave propagation · Site-City Interaction · Spatial variability · Local seismic response · Numerical modelling
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1051 8-020-00965-2) contains supplementary material, which is available to authorized users. * C. Varone [email protected]; [email protected] Extended author information available on the last page of the article
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Bulletin of Earthquake Engineering
1 Introduction Strong earthquakes have recently affected densely urbanized areas, leading to a high level of urban destruction: Italy 2009 ( ML ≈ 5.9), Haiti 2010 ( MW ≈ 7.0), Chile 2010 ( MW ≈ 8.8), New Zealand 2011 (ML ≈ 6.3), Nepal 2015 (ML ≈ 7.8) and Italy 2016 (ML ≈ 6.0). These areas are diffusely built in complex geological contexts, responsible for various seismic site effects. Local heterogeneity of the subsoil causes vertically and horizontally seismic impedance contrasts due to the different mechanical properties of the alluvial deposits in urban areas (i.e. basins, valleys, and canyons). Such site effects derive from physical phenomena such as 1D re
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