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Estimating site amplification factors from ambient noise
Author(s) -
Taylor Steven R.,
Gerstoft Peter,
Fehler Michael C.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl037838
Subject(s) - amplitude , ambient noise level , forcing (mathematics) , noise (video) , seismic noise , geology , seismic array , resonance (particle physics) , wavenumber , harmonic oscillator , nonlinear system , physics , oscillation (cell signaling) , computational physics , seismology , acoustics , atmospheric sciences , optics , atomic physics , chemistry , artificial intelligence , computer science , image (mathematics) , sound (geography) , biochemistry , quantum mechanics
We present a methodology to obtain frequency‐dependent relative site amplification factors using ambient seismic noise. We treat a seismic network or array as a forced damped harmonic oscillator system where each station responds to a forcing function obtained from frequency‐wavenumber beams of the ambient noise field. A network or array beam is necessary to estimate the forcing function. Taken over long time periods, each station responds to the forcing function showing a frequency‐dependent resonance peak whose amplitude and spectral width depends upon the elastic and anelastic properties of the underlying medium. Our results are encouraging in that hard rock sites show little variability and have narrower resonance peaks with reduced amplitudes relative to soft rock sites in sedimentary basins. There is much more variability observed at soft rock sites and a tendency for spectral peaks to shift to higher frequencies and become broader as the site amplification increases. This could be due to due to lower densities and/or small‐strain nonlinearity at stations having high site amplification.