caa a22 4500 445846917 CHVBK 20180317145401.0 cr unu---uuuuu 170323e20110601xx s 000 0 eng 10.1007/s10518-011-9266-2 doi (NATIONALLICENCE)springer-10.1007/s10518-011-9266-2 Frequency variation in site response as observed from strong motion data of the L'Aquila (2009) seismic sequence [Elektronische Daten] [R. Puglia, R. Ditommaso, F. Pacor, M. Mucciarelli, L. Luzi, M. Bianca] Previous works based mainly on strong-motion recordings of large Japanese earthquakes showed that site amplification and soil fundamental frequency could vary over long and short time scales. These phenomena were attributed to non-linear soil behaviour: the starting fundamental frequency and amplification were both instantaneously decreasing and then recovering for a time varying from few seconds to several months. The recent April 6, 2009 earthquake (M W 6.3), occurred in the L'Aquila district (central Italy), gave us the possibility to test hypotheses on time variation of amplification function and soil fundamental frequency, thanks to the recordings provided by a pre-existing strong-motion array and by a large number of temporary stations. We investigated the intra- and inter-event soil frequency variations through different spectral analyses, including time-frequency spectral ratios and S-Transform (Stockwell etal. in IEEE Trans Signal Process 44:998-1001, 1996). Finally, analyses on noise recordings were performed, in order to study the soil behaviour in linear conditions. The results provided puzzling evidences. Concerning the long time scale, little variation was observed at the permanent stations of the Aterno Valley array. As for the short time-scale variation, the evidence was often contrasting, with some station showing a time-varying behavior, while others did not change their frequency with respect to the one evaluated from noise measurements. Even when a time-varying fundamental frequency was observed, it was difficult to attribute it to a classical, softening non-linear behaviour. Even for the strongest recorded shocks, with peak ground acceleration reaching 0.7g, variations in frequency and amplitude seems not relevant from building design standpoint. The only exception seems to be the site named AQV, where the analyses evidence a fundamental frequency of the soil shifting from 3Hz to about 1.5Hz during the mainshock. Springer Science+Business Media B.V., 2011 Strong motion nationallicence Subsoil non-linearity nationallicence Horizontal to vertical spectral ratio nationallicence Standard spectral ratio nationallicence 1D modeling nationallicence S-Transform nationallicence Puglia R. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut Ditommaso R. Di.S.G.G., University of Basilicata, Potenza, Italy aut Pacor F. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut Mucciarelli M. Di.S.G.G., University of Basilicata, Potenza, Italy aut Luzi L. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut Bianca M. Di.S.G.G., University of Basilicata, Potenza, Italy aut Bulletin of Earthquake Engineering Springer Netherlands 9/3(2011-06-01), 869-892 1570-761X 9:3<869 2011 9 10518 https://doi.org/10.1007/s10518-011-9266-2 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10518-011-9266-2 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Puglia R. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut NATIONALLICENCE 700 1- Ditommaso R. Di.S.G.G., University of Basilicata, Potenza, Italy aut NATIONALLICENCE 700 1- Pacor F. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut NATIONALLICENCE 700 1- Mucciarelli M. Di.S.G.G., University of Basilicata, Potenza, Italy aut NATIONALLICENCE 700 1- Luzi L. Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy aut NATIONALLICENCE 700 1- Bianca M. Di.S.G.G., University of Basilicata, Potenza, Italy aut NATIONALLICENCE 773 0- Bulletin of Earthquake Engineering Springer Netherlands 9/3(2011-06-01), 869-892 1570-761X 9:3<869 2011 9 10518 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer