Estimating site amplification factors from ambient noise

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...

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Bibliographic Details
Published in:Geophysical research letters 2009-05, Vol.36 (9), p.L09303-n/a
Main Authors: Taylor, Steven R., Gerstoft, Peter, Fehler, Michael C.
Format: Article
Language:English
Subjects:
ambient noise
Amplification
Arrays
Beams (radiation)
Earth sciences
Earth, ocean, space
Earthquake ground motions and engineering seismology
Earthquakes
Exact sciences and technology
Geology
Networks
Noise
Physical properties
Physical Properties of Rocks
Rock
Rocks
Seismology
site factors
Spectra
Stations
Surface waves
Surface waves and free oscillations
Wave attenuation
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Summary: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.
ISSN:0094-8276
1944-8007
DOI:10.1029/2009GL037838