GNGTS 2013 - Atti del 32° Convegno Nazionale

Preliminary HVSR analysis in the historical centre of Ferrara, Northern Italy N. Abu Zeid, F. Albertin, S. Bignardi, G. Santarato Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara Introduction. Following the earthquake sequence started on May 20 th 2012, 7 earthquakes of local magnitude > 5.0, culminated by two main shocks with Ml: 5.9 and 5.8, struck the Emilia area, North Italy. The main event, took place on the 20 th of May 2012, had instrumental hypocentre located at few kilometres from the towns of Mirandola, Finale Emilia and Bondeno, and about 30 km west of the city of Ferrara, while the later was located at about 12 km (INGV, Italy) to the SW of the main shock. The occurrence of these earthquakes and the associated damage, together with widespread liquefaction phenomena has urged the need to accelerate the measures to help in the microzonation of the whole territory of the Po Alluvial Plain. Although no clear liquefaction events had occurred in the historical centre of Ferrara, noticeable damage occurred to the building, including the Medieval Castel of Ferrara among others. Most of these buildings are founded on a small paleo-river ridge that crosses the city centre from NE to SW where it enters grate paleo-river ridge of the ancient course of the Po River passing through and crossing the south and south-western part of the historical city centre. In these paleo-river ridges friable and saturated sand sediments are present (Fig. 1). Taking into consideration the needs for actions to aid in the microzonation, a single station campaign was undertaken in the historical centre of the city of Ferrara, North Italy, to collect passive seismic noise at different Fig. 1 - Simplified geological map of the historical centre of the city of Ferrara (North Italy). Blue crosses: single station test site, asterisk: school building, dark green colour: sand and silt deposits of the Po River delta plain, light green colour: mainly clay and sand with some organic clay sediments belonging to the Po River delta plain (kindly provided by Marco Stefany). On the same map find reported the encountered typical site resonance frequencies (F 0 ). 167 GNGTS 2013 S essione 2.2