Attempt to detect combination tones between the Earth's free oscillation and the Earth tide,II -Bispectral Analysis-

• Main Authors: Tanaka,Toshiyuki, Furumoto,Muneyoshi
• Format: Report
• Language: English
• Published: Faculty of Science, Kanazawa University/Faculty of Science, Kanazawa University 1998
• Subjects: nonlinear elasticity; the free oscillation; the earth tide; combination tone; bispectrum; Syowa Station; Antarc*; Antarctica; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3017; http://id.nii.ac.jp/1291/00003017/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3017&item_no=1&attribute_id=18&file_no=1

Two elastic oscillations at frequencies f_1 and f_2 in an elastically nonlinear material can produce combination tones at the sum (f_1+f_2) and the difference (f_1-f_2) frequencies. If the nonlinearity in the earth's interior is sufficiently large, such phenomena can be observed in the earth's oscillations. Analyzing long-period seismograms recorded by a superconducting gravimeter installed at Syowa Station in Antarctica, we try to detect the combination tones between the earth's tides and the spheroidal free oscillations. The method employed here is bispectral analysis. Since the bispectrum represents the coherency among three components with frequencies of f_1, f_2 and f_1+f_2, it is a powerful tool to analyze the combination tones. The results suggest that the spheroidal oscillations _0S_0 and _0S_5 modes probably interact with the ter-diurnal and diurnal tides, respectively.