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First Observation of the Earth's Permanent Free Oscillations on Ocean Bottom Seismometers
Author(s) -
Deen M.,
Wielandt E.,
Stutzmann E.,
Crawford W.,
Barruol G.,
Sigloch K.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl074892
Subject(s) - seismometer , geology , seismology , ocean bottom , seafloor spreading , geophysics , microseism , noise (video) , tilt (camera) , nutation , geodesy , physics , mechanical engineering , astronomy , artificial intelligence , computer science , engineering , image (mathematics)
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 autocorrelation 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.