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Modelling secondary microseismic noise by normal mode summation
Language
English
Obiettivo Specifico
1T. Geodinamica e interno della Terra
Status
Published
JCR Journal
JCR Journal
Title of the book
Issue/vol(year)
/193(2013)
ISSN
0956-540X
Electronic ISSN
1365-246X
Publisher
Wiley-Blackwell
Pages (printed)
1732-1745
Issued date
2013
Abstract
Secondary microseisms recorded by seismic stations are generated in the ocean by the interaction
of ocean gravity waves.We present here the theory for modelling secondary microseismic
noise by normal mode summation.We show that the noise sources can be modelled by vertical
forces and how to derive them from a realistic ocean wave model. We then show how to
compute bathymetry excitation effect in a realistic earth model by using normal modes and
a comparison with Longuet–Higgins approach. The strongest excitation areas in the oceans
depends on the bathymetry and period and are different for each seismic mode. Seismic noise
is then modelled by normal mode summation considering varying bathymetry. We derive an
attenuation model that enables to fit well the vertical component spectra whatever the station
location. We show that the fundamental mode of Rayleigh waves is the dominant signal in
seismic noise. There is a discrepancy between real and synthetic spectra on the horizontal
components that enables to estimate the amount of Love waves for which a different source
mechanism is needed. Finally, we investigate noise generated in all the oceans around Africa
and show that most of noise recorded in Algeria (TAM station) is generated in the Northern
Atlantic and that there is a seasonal variability of the contribution of each ocean and sea.
of ocean gravity waves.We present here the theory for modelling secondary microseismic
noise by normal mode summation.We show that the noise sources can be modelled by vertical
forces and how to derive them from a realistic ocean wave model. We then show how to
compute bathymetry excitation effect in a realistic earth model by using normal modes and
a comparison with Longuet–Higgins approach. The strongest excitation areas in the oceans
depends on the bathymetry and period and are different for each seismic mode. Seismic noise
is then modelled by normal mode summation considering varying bathymetry. We derive an
attenuation model that enables to fit well the vertical component spectra whatever the station
location. We show that the fundamental mode of Rayleigh waves is the dominant signal in
seismic noise. There is a discrepancy between real and synthetic spectra on the horizontal
components that enables to estimate the amount of Love waves for which a different source
mechanism is needed. Finally, we investigate noise generated in all the oceans around Africa
and show that most of noise recorded in Algeria (TAM station) is generated in the Northern
Atlantic and that there is a seasonal variability of the contribution of each ocean and sea.
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