Assessing the Main Frequencies of Modern and Historical Buildings Using Ambient Noise Recordings: Case Studies in the Historical Cities of Crete (Greece)

Monitoring seismic structural response is an essential issue in earthquake risk assessments and mitigation studies for monumental buildings in order to undertake earthquake disaster management. This study aims at identifying the resonant frequency of soil and modern and historical buildings in three major municipalities of Crete (Heraklion, Chania, and Rethymno) using ambient noise recordings (microtremors) considering the importance of soil–structure interaction to seismic structural response, particularly for historical buildings and monumental structures. In this study, ambient noise recordings have been processed through Horizontal to Vertical Spectral Ratios (H/V) to preliminarily examine the main frequencies and to examine whether the building has its main frequency close to that of the soil in order to identify potential resonance phenomena. Numerous ambient noise recordings were recorded on the soil, in the basement, and at each n-floor of the buildings. The incorporation of local site conditions and soil-building resonance phenomena into the urban planning development of Crete regarding earthquake risk assessments is necessary. In this direction, microtremors can be used as an effective tool to support civil protection preparation and operational decision-making in terms of earthquake disaster, specifically in the area of Crete, which is characterized by high seismic activity and a high cultural monuments capacity.