GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Evaluation of the topographic amplification factors along a cross-section of the San Luca hill, Bologna: comparison between one- and two-dimensional models of local seismic response S. Bonini, S. Castellaro, M. Di Donato, G. Lattanzi Università di Bologna – Dip. Scienze Biologiche, Geologiche e Ambientali (BIGEA) Abstract The seismicity of the Emilia region and the Bologna area was very underestimated by the public opinion before the 2012 seismic crisis. However, several seismogenic sources had already been recognized and investigated by the seismological world (DISS working group, 2018). By the way, historical sources testify to the occurrence of several strong earthquakes since the 12th century. The city of Bologna and the neighboring municipalities were affected by seismic sequences lasting several months in 1504-1505, 1779-1780, 1881 and 1929 (Guidoboni et al., 2003). The same sources report that the greater level of damage occurred in the northern area of the historical center. The reliability of this historical report was investigated by Benvenuto (2016) and, as the city center can be considered flat, it was sufficient to use numerical modeling of one-dimensional seismic response. These seismic events also affected the south-western part of Bologna, including the hill which the sanctuary of Madonna di San Luca stands on (also known as Colle della Guardia). The first ascertained damages for the structure – whose construction, begun in 1741, was completed only in 1765 – occurred during the seismic sequence of 1779-1780. In this work we focus on the south-western area of the city, which goes from the Colle della Guardia to the Dall’Ara Stadium, situated near the foot of the hill slope, with a cross-section of 2.5 km in length. Here the topography suggests the need for two-dimensional local seismic response modeling [Figure 1]. The study of available geological maps allowed us to create a geological model for the proposed section. It was followed by a campaign of geophysical investigations that drove the reconstruction of the mechanical properties of each identified seismic layer (such as shear stiffness and the impedance contrasts of main outcropping lithotypes).