First Observation of the Earths Permanent Free Oscillations on Ocean
Bottom Seismometers - Wonder of some upper harmonics get felt or heard
by human's? Especially if fluid in their ear(s) .... rumors suggest some
animals can perceive such 'sounds' ..... Would any of you consider this
RFI? ;-)
https://www.livescience.com/61154-earth-hum-recorded-underwater.html -
Earth's Mysterious Hum Recorded Underwater for 1st Time 12/11/17
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074892/abstract -
First Observation of the Earth's Permanent Free Oscillations on Ocean
Bottom Seismometers 11/14/17
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Abstract
The Earth's hum is the permanent free oscillations of the Earth recorded
in the absence of earthquakes, at periods above 30 s. We present the
first observations of its fundamental spheroidal eigenmodes on broadband
ocean bottom seismometers (OBSs) in the Indian Ocean. At the ocean
bottom, the effects of ocean infragravity waves (compliance) and
seafloor currents (tilt) overshadow the hum. In our experiment, data are
also affected by electronic glitches. We remove these signals from the
seismic trace by subtracting average glitch signals; performing a linear
regression; and using frequency-dependent response functions between
pressure, horizontal, and vertical seismic components. This reduces the
long period noise on the OBS to the level of a good land station.
Finally, by windowing the auto correlation to include only the direct
arrival, the first and second orbits around the Earth, and by
calculating its Fourier transform, we clearly observe the eigenmodes at
the ocean bottom.
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