[RFI] Low Freq Observation of Earths Oscillations on Ocean Bottom Seismometers 121217

[WD8ARZ]

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.