  The polar motion data is analyzed to obtain accurate position of the figure
axis referred to the Earth-fixed frame. The variation of the figure axis should
be the basic object to which the geophysical events are linked. By the method
of rigid dynamics, the relation between the rotational and the figure axes is
derived. The polar motion is the motion of the rotational axis on the Earth's
surface and therefore the exact position of the figure axis on the surface at
each moment is obtained from the polar motion. Since the accuracy of the recent
data for the polar motion is very high, the obtained position of the figure
axis is considered to keep good quality. As an average for a long duration of
time, the obtained figure axis exhibits stable annual and semi-annual
variations while it has no component with the period of the Chandler wobble.
Besides this general feature, it shows different patterns from year to year as
well as small irregularities with shorter periods, most of which are considered
to be significant but not attributed to the observational errors. Further, a
simple model is introduced for the cause of the seasonal variation of the
figure axis. The model explains both the variation of the figure axis obtained
above and that of the rotational speed which is so far known.
