L'Aquila earthquake (April 6th 2009, Central Apennine, Italy): site effect, coseismic evidence and historical development of the Collebrincioni area

The village of Collebrincioni is located right at the center of the most damaged area of the April 6th 2009 L’Aquila earthquake. It is known from historical data that this site had been heavily affected by the 1461 and 1703 seismic events and for that reason remained abandoned for a long time; the area has been settled again at the end of the 18th century with the rebuilding of the present conurbation in a new safer location. After the April 6th 2009 earthquake many evidences of coseismic effects have been found around the Collebrincioni surroundings, even though the macroseismic intensity calculated in the new settlement was found to be moderate (6 MCS). The aim of this work is to verify whether the cause of the migration from the old location can be linked to site effects; for this purpose, several measurements of horizontal to vertical spectral ratio (HVSR) have been carried out at various locations to obtain information on amplification phenomena. To allow a quick evaluation of site seismic response, without requesting any information about stratigraphical and geotechnical properties of the foundation soils, the Nakamura’s technique was adopted in this paper. Measurements of HV spectral ratio carried out in the area show relevant differences between the new and the ancient settlements confirming the hypothesis that the abandonment of the old Collebrincioni settlement can be related to the site effects which have amplified the destructive effects of the earthquakes.