The spectrum of Earth's free oscillations is split not only by the rotation and ellipticity but by unknown strucutre within the Earth. The anomalous splitting is a phenomenon that the splitting is larger than predicted by the rotation and ellipticity. Although the cause of the anomalous splitting has been uncertain, Woodhouse et al. [1986> have proposed an interpretation in terms of the anisotropy in the inner core. In this letter, we examine an alternative interpretation in terms of the rigidity in the outer core. ¿ American Geophysical Union 1989