The Earth Inner Core Translation Oscillation: Theory And Detection

The Earth inner core translational oscillation means the solid inner coretranslational oscillate in the liquid outer core, and refered as Slichter mode; the eigenperiods of it can provide the directly constraints on the density jump at the inner core boundary (ICB). Although many reseachers have studies this mode from the 1960s, there is no signal has been confiremed as the Slichter mode, the detection of the Slichter mode is still a pending thing.In this study, for the first time (in China), we introduce the subseismic approximation theory for the calculations of the eigenperiods of the Slichter mode in detail, and we also autonomously carry out this theory, the calculated eigenperiods of this study are consistent with those of the previous studies which based on the different theories and methods. After this, we introduce how to remove the known signals (air press, tides, and rotation effects) from the original SG records, and how to use the Tsoft package to remove the ocean tide effects. According to the results obtained by using different methods to remove the tide signals from the observed SG records, we confirm that the simultaneously harmonic analysis of the gravity records and the local air-press records is a more powerful way. The pretreatment processes introduced in this study are quite universal, and can be chosen as a standred reference for any surface gravity observations.Finally, based on the SG records between 2010/4/15 to 2011/7/17, about 11000 hours, after removing the tide and local air-press effects, we use the OSE method to search for the Slichter mode, and after very strict selections, we find one candidate set with the periods: 4.310±5.7－10-3(/n=-1),3.914±6.4×10-3(m=0), and 3.642±5.1×10-3(/n=+1) hours. We consider that this signal set might be the splitting signals of the Slichter mode, and based on it, we obtain that the density jump at ICB of the PREM model should be ΔρICB=1240.6 kg/m3, while 727.3 kg/m3 is given by the PREM model, our estimation may probide new constarin on refining the Earth model.