GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Comparison between the 1D analysis, carried out in the site of the DH test nearest the profile, and the 2D analysis shows that the PGA estimated with 1D analysis is 18% lower than that estimated with the 2D analysis; similarly, the amplification calculated with 1D analysis in the 0.1s<T<0.5s, range including the main period of the damaged building, is 11÷12% lower. Thus, 1D analyses, in valleys with irregular or highly variable substratum geometry, can lead to significant underestimations of the amplification of the seismic motion at the surface. For an estimation of the shaking in absolute values, as required by regional guidelines (DGR 564/2021), the HSM parameter was also determined (Naso et al., 2019). The 2D analysis has shown that in the central part of the valley HSM is 0.88 g, indicative of a high seismic hazard, according to the classification recently proposed by the Technical Commission for Seismic Microzonation (CT, 2022), while towards the east and west the hazard decreases, HSM=0.55÷0.60 g, up to the edges of the valley, where HSM has values between 0.34 and 0.4 g, indicative of a medium level hazard. Conclusions The in-depth studies carried out to explain the damage observed in Castelnovo ne' Monti following the Lunigiana seismic sequence of 21-30 June 2013 have shown that the area of interest is susceptible to two-dimensional local effects, due to the strong variation in the of the cover and depth of the substratum, made irregular by a buried fault. The comparison of 2D and 1D analyses showed a considerable underestimation of the amplification and shaking values calculated with the 1D analyses. The advisability of 2D analyses for a more correct estimation of local seismic hazard, in this as in other similar cases, can already be inferred from an examination of topographic and basic geological maps, which faithfully map landforms, detrital covers and tectonic structures that dislocate the substratum. Bibliography Beretti P. (2013): Indagini geognostiche e geofisiche dell’area in Castelnovo ne’ Monti danneggiata dal sisma del 21/06/2013. Archive of the “Ufficio Lavori Pubblici e Patrimonio”, Municipality of Castelnovo ne' Monti. CT (2022): Microzonazione sismica. Linee guida per la gestione del territorio in aree interessate da amplificazione. Versione 2.0. Technical Commission on Seismic Microzonation, Civil Protection Department and Conference of Regions and Autonomous Provinces of Italy, Rome, 2022 DGR 564/2021: Integrazione della propria deliberazione n. 476 del 12 aprile 2021 mediante approvazione dell’allegato A, “Atto di coordinamento tecnico sugli studi di microzonazione sismica