The effect of local wind on seismic noise near 1 Hz at the MELT site and in Iceland
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Útgefandi
The Seismological Society of America
Úrdráttur
The mantle electromagnetic and tomography (MELT) experiment on the
east Pacific rise near 17°S was the first large teleseismic experiment on a midocean
ridge. During the six-month deployment, no compressional arrivals were well recorded
above 0.5 Hz. In comparison, the ICEMELT experiment in Iceland recorded
compressional arrivals at 1-2 Hz from about 2 earthquakes per month. We compare
noise spectra from the two experiments and show that this difference in detection is
at least in part a result of noise. Near 1 Hz, seismic noise in the oceans is produced
locally by wind-generated waves. At both experiment sites, 1-Hz noise levels are
well correlated with local sea-surface-wind speeds derived from satellite observations.
For a given wind speed, 1-Hz noise levels are about 10-20 dB lower in Iceland.
At the MELT site, cross-correlations of wind speed with the logarithm of noise in a
narrow-frequency band yield correlation coefficients exceeding 0.7 at frequencies
between 0.4 Hz and 2 Hz. Noise levels at 1 Hz increase with wind by 1.3-1.4 dB
per m/sec for wind speeds less than 10 m/sec. For the ICEMELT experiment, high
correlation coefficients extend to markedly higher frequencies for coastal stations,
and there is a 10-dB drop in 1-Hz noise levels 100-km inland. Noise levels increase
by about 0.8 dB per m/sec. The strong correlation between wind speed and l-Hz
seismic noise provides justification for using satellite wind speed data to search for
locations on the global spreading system where there is a better probability of recording
high-frequency arrivals. The calmest sites are found on the northern east
Pacific rise, near the equator in all oceans, and near 34 ° N and 22 ° S on the mid-
Atlantic ridge.
Lýsing
Efnisorð
Jarðmöttull, Jarðeðlisfræði, Sneiðmyndatökur, Jarðskjálftar, Jarðskjálftamælingar
Citation
William S. D. Wilcock, Spahr C. Webb, Ingi Þorleifur Bjarnason. (1999). The effect of local wind on seismic noise near 1 Hz at the MELT site and in Iceland. Bulletin of the Seismological Society of America, 89(6), 1543-1557.