Detection of the Inner Core Translational Triplet Using Superconducting Gravimetric Observations

Based upon seven superconducting gravimeter (SG) records of 20 000 h length after the 2004 Sumatra earthquake, four methods, namely the ensemble empirical mode decomposition (EEMD), the multi-station experiment (MSE) technique, the autoregressive (AR) method and the product spectrum analysis (PSA) method, are chosen jointly together to detect the inner core translational modes (₁S₁). After the conventional pretreatment, each of the seven simultaneous residual gravity series is divided into five segments with an 80% overlap, and then EEMD is applied to all the 35 residual SG series as a dyadic filter bank to get 35 filtered series. After then, according to different stations and different time windows, five new simultaneous gravity datasets are obtained. After using MSE for each of the five new datasets, the AR method is used to demodulate some known harmonic signals from the new sequences that obtained by using MSE, and three demodulated product spectra are obtained. Then, according to two criterions, two clear spectral peaks at periods of 4.548 9±2.3×10⁻⁵ and 3.802 3±3.2×10⁻⁵ h corresponding respectively to the singlets m=−1 and m=+1 are identified from various spectral peaks, and they are close to the predictions of the 1066A model given by Rieutord (2002), but no spectral peak corresponding to the singlet m=0 is found. We conclude that the selected two peaks might be the observed singlets of the Slichter triplet.