Stripping the narrowband coupled multiplets based on seismic records using the OSE

The splitting and coupling observations for the normal modes may reveal details about large-scale structure of the 3D Earth. In the frequency domain, especially for frequency >1.5 mHz, the mode-coupling should be taken into account as the modes become denser and closer. There are many S-S type clusters below 3 mHz which need to be resolved, such as 0S7-2S3, 1S5-2S4, 4S1-0S8-3S3, 0S9-1S0, 1S7-2S6 and other similar clusters. This paper explores whether the obtained splitting singlets of normal modes in high frequency band have higher SNRs and precision under the condition of considering coupling effects into the optimum sequence estimate (OSE). On the basis of the OSE method, we started experiments by extending the equations for vertical and transverse components to the group-coupling scheme that the splitting coefficient matrix B is not only determined by a target multiplet alone but also includes several cross-coupling multiplets. Then the results of self-coupling and group-coupling of the singlets are compared to determine whether the across-multiplet coupling plays an important role in the stripping of the modes. The results showed that the singlets of higher modes could be observed more clearly and resolved more completely by considering group-coupled modes for the narrow-band frequency. After comparing observations with predictions of the PREM−tidal model, the differences may provide valuable information about the deep Earth and further constraints on the 3D structure of the Earth.