Evaluation of complex site effects through experimental methods and numerical modelling: The case history of Arquata del Tronto, central Italy

This work deals with the experimental and numerical evaluation of the local seismic response of Arquata del Tronto area (Marche Region, central Italy), severely struck by the Mw 6.0 August 24th, 2016 earthquake. Arquata main village rises on elongated WNW-ESE-trending ridge of the central Apennines thrust-belt (central Italy), at elevations about 170 m higher than the underlying alluvial valleys where Borgo and San Francesco hamlets are built on. Despite their proximity (less than 500 m), Arquata del Tronto, Borgo and San Francesco reported a different damage distribution after the August 2016 mainshock, suggesting that the seismic response of the area may be controlled by site effects. In order to explore this hypothesis, we evaluated the 2D numerical local seismic response along four representative geological cross-sections passing through Arquata del Tronto, San Francesco and Borgo. Additional 1D analyses were carried out at strategic points along the cross-sections in order to explore the 2D physical phenomena governing the local response. The satisfactory agreement between numerical amplification functions in linear range and experimental amplification functions obtained by the Generalized Inversion Technique (GIT) applied to a large number of aftershocks confirms the substantial reliability of the subsoil models. Numerical analyses representative of the 2016 mainshock were carried out and processed in terms of peak and key ground motion parameters. A comparison with the damage induced by the 2016 mainshock was finally undertaken substantially justifying the observed pattern. This study provides general implications about site response and seismic microzonation in sites characterized by similar complex geological and morphological settings.