Modellazione numerica bidimensionale della risposta sismica nel comune di Accumoli

In the present study the evaluation of the local seismic response of the Municipality of Accumoli (RI) was carried out through a bidimensional numerical modeling along a geological cross section in the valley of the Tronto River. The here performed modelling integrates the results from previous studies aimed at level 3 seismic microzonation after the 2016-2017 seismic sequence in Central Italy, obtained for a Return Time (RT) of 475 years only. From the geological point of view, the study area is characterised by an alluvial body composed of clastic soils ascribable to river terraces and fluvial deposits overlaying a marly-arenaceous bedrock, represented by the Flysch della Laga Formation. Amplification functions were obtained via 2D numerical modelling that allowed to analyze the seismic amplification of the study area, for RT of 975 and 2475 years. The numerical outputs were obtained through the LSR2D software (by Stacec S.r.l.): a discretization in triangular meshes with a resolution of 3 m, free-field conditions to the lateral boundaries of the model and a kinematic constraint on the vertical motion at the base of the numerical domain (inside the seismic bedrock) were assumed. Moreover, an equivalent linear solution was adopted and a visco-elastic rheological behavior was attributed to the considered material. A one-dimensional modeling (by STRATA software) was also performed to compare the results with the ones derived from the 2D modeling. The 1D and 2D amplification functions highlighted that the maximum seismic amplification peaks correspond to the middle portion of the valley, which is also characterized by a mainly 1D seismic response, while a not negligible contribution of surface waves propagating from the edges of the alluvial basin can be recognised close to its boundaries. Amplification factors (FA) and elastic response spectra were also obtained along the modelled section. In particular, the computed values of FA, related to the period range 0.1-0.5 s (the most relevant for civil engineering design), were used for the seismic microzonation mapping referred to TR 975 and 2475. The decreasing FA values at the higher TR is justified as a consequence of the more intense non-linear effects. The here experienced methodology, can be regarded as a guideline for further studies of local seismic response, where a similar geological and morphological setting can be surveyed, as well as a reliable tool for seismic risk mitigation in frameworks of urban planning and building design.