Search for the Slichter modes based on a new method: Optimal sequence estimation

Abstract

The inner core translational mode (1S1), known as the Slichter triplet, can provide important information particularly on the Earth's inner core and its dynamics. A time domain spectral analysis method, the optimal sequence estimation (OSE), is devised and applied to search for the Slichter modes. Applications of the OSE and the multistation experiment (MSE) technique for detection of the singlets of 3S1 and 2S1 show that both OSE and MSE can isolate their singlets, but OSE provides a higher signal-to-noise ratio. OSE also can completely isolate the modes 0S2 and 1S2. Using two superconducting gravimeter data sets from nine Global Geodynamic Project stations before and after the 2004 Sumatra earthquake, we search for the possible Slichter triplet via OSE and provide a simple validation using the product spectrum. We set two preliminary criteria in order to identify possible signals; results show three signals as candidates for the Slichter triplet, more likely in the data after the 2004 Sumatra earthquake. While choosing the most reasonable criteria needs further studies, we emphasize here the effectiveness of the OSE in searching for the Slichter modes rather than claiming actual detections. Key Points Optimal sequence estimation (OSE) for search for Slichter modes is put forwardValidity of OSE is confirmed by isolating all singlets of 2S1, 3S1, 0S2 and 1S2Three possible singlets of Slichter modes (m equals -1,0 and +1) were suggested © 2013. American Geophysical Union. All Rights Reserved.