GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Figure 2 a) Oriented collapse toward the south of the back wall of the northern stoa at Segesta; (b) an arch fell down in the same direction of the back wall; c) Column of the stoa in the eastern wing, the portion highlighted in blue represents a broken corner in the column drums; d) offset in steps; e) rotated basal drums. Seismostratigraphic model and Local Seismic Response The destructive seismic events that affected the studied area in the past have caused several damage of different intensities to the buildings. A heterogeneous distribution of the damage caused by each event was observed. These effects, in addition to the intrinsic differences in the seismic vulnerability of the buildings, can be mainly attributed to different seismic motion amplification effects induced by local geological and geomorphological conditions. In fact, when a seismic motion propagates from the bedrock to the surface, it can change in amplitude, duration and frequency spectrum, due to the local geological characteristics of the site (Lanzo, 1999). At the scale of the single structure or geotechnical system, the Local Seismic Response (LSR) allows to define the changes of a seismic signal, due to the aforementioned factors, with respect to that of a rigid reference site with a horizontal topographic surface. To this purpose, a seismostratigraphic model has been reconstructed using a combined method of multichannel analysis of surface waves (MASW) and ambient noise array measurements to determine horizontal to vertical component spectral ratios (HVSR). The aim of MASW surveys was to reconstruct S-waves velocity profiles by surface waves dispersion spectrum analysis, while HVSR method allowed to obtain information about frequencies for which site effects of resonance and seismic amplification can occur (e.g. Mucciarelli and Gallipoli, 2001; Lunedei and Malischewsky, 2015). 16 HVSR registrations and 10 MASW surveys have been carried out, in the three studied areas of the site (see fig. 1a). The combined use of these two seismic methods allowed the inversion of the HVSR curves, constrained by MASW results, producing a robust and detailed subsoil velocity model.