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Incessant excitation of the Earth's free oscillations: global comparison of superconducting gravimeter records |
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| Authors: | Kazunari Nawa Naoki Suda Yoshio Fukao Tadahiro Sato Yoshiaki Tamura Kazuo Shibuya Herbert McQueen Heikki Virtanen Jussi Kriinen |
| Institution: | a Geological Survey of Japan, Higashi 1-1-3, Tsukuba 305-8567, Japan b Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashihiroshima 739-8526, Japan c Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo 113-0032, Japan d National Astronomical Observatory, Hoshigaoka 2-12, Mizusawa 023-0861, Japan e National Institute of Polar Research, Kaga 1-9-10, Itabashi, Tokyo 173-8515, Japan f Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia g Finnish Geodetic Institute, Geodeetinrinne 2, Masala FIN-02430, Finland |
| Abstract: | Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsähovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band. |
| Keywords: | Background free oscillations Noise level SG IDA GEOSCOPE |
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