Peak Frequency Changes From HV Spectral Ratios in Central Italy: Effects of Strong Motions and Seasonality Over 12 Years of Observations

We analyzed 12 years of continuous seismic data acquired by two stations in Central Apennines (Italy) with the aim to investigate temporal variations H/V spectral ratios. The are located epicentral areas main strong motion earthquakes occurred Italy last (L’Aquila 06 April 2009, Mw 6.1; Amatrice 24 August 2016, 6.0; Visso 26 October 5.9, and Norcia 30 6.5). ratios computed both on recorded stations. subjected abrupt changes after earthquakes. results highlight that shaking, there remarkable drops peak frequencies (7%–10% reduction). After this sudden decrease, frequency slowly recovers initial value a time ranging from few months years. also observe moderate variation (of order 2%–3%) linked seasonal variations: increase spring-summer decrease during winter. have been interpreted terms velocity shallow layers. This effect must be taken into account for microzonation, geophysical, engineering studies often carried out analysis over proved useful procedure highlighting relating properties layers propagation medium could provide relevant information site characterization permanent