Local seismic response of the Quadriportico of the Basilica of Saint Paul Outside the Walls in Rome

The Basilica of Saint Paul Outside Walls is one of the four papal basilicas in Rome, the largest after Saint Peter's in the Vatican. The facade of the church is preceded by a large Quadriportico, designed and built in the thirties of the last century. The Quadriportico is a monumental architectural structure, measuring 70 m on each side. The Basilica and the Quadriportico stand on a flat area on the left bank of the Tiber River. This area has been affected by several earthquakes throughout history, notably those in 442, 801, and 1351 AD, which caused significant damage to the Basilica. More recently, the Central Italy mainshock of 2016 (Mw=6.5) caused slight damage to the Quadriportico. Over the years, several geotechnical investigations have been conducted to characterize the subsoil characteristics and determine its main geotechnical properties. As part of a national research project, a recent investigation focused on defining the dynamic soil properties through both laboratory and in-situ testing. The data collected was used to develop a geotechnical model for seismic response analyses, carried out using one-dimensional (1-D) numerical code. The results of these analyses were then compared with codebased response spectra at the ground surface. The findings and their implications for the seismic protection of the monuments are examined and discussed.