Abstract：In this study, we select 15 sets of 18 of superconducting gravimeter (SG) records from GGP (global geodynamics project) stations after the 2004 Sumatra Mw 9.0 earthquake and use EEMD (ensemble empirical free oscillations mode (3S1, 0S4, 0S5) and their spectral splitting with frequencies less than 1 mHz. After removing the tidal and local atmospheric pressure effects from the original minute-interval SG records, we obtain a residual gravity data set. Then, EEMD is applied to this SG time-series to obtain different IMF (intrinsic mode function) on different frequencies. This will significantly reduce the possibility of mode mixing and end effect, and it could improve some low-frequency seismic signals’ SNR (signal-to-noise ratio). Therefore, EEMD could enable some splitting spectral of low-frequency free oscillation signals to be observed more clearly. Through comparisons of the normalized amplitude of the results obtained without using EEMD and after using EEMD of the residual gravity records, the experimental results show that when EEMD is applied to residual gravity records, it can be more effective for observation of the Earth’s low-frequency signals and will obtain higher resolution of low-order spherical oscillations’ singlets. This study demonstrates that EEMD is effective in data-processing and that the superconducting gravimeter is superior in detecting the low-order earth’s free oscillations.
ZENG Shiyu,SHEN Wenbin. Observation of Ultralow-Frequency Earth Free Oscillation Mode Multi-Splitting Based on EEMD and Global Superconducting Gravimeter Data：A Case Study[J]. jgg, 2016, 36(8): 689-702.
