Furthermore, the maximum seismic-velocity axis is tilted about 10 degrees relative to Earth's rotation axis, allowing seismologists to identify a slow eastward motion of this feature, such that it rotates once every 400 years relative to Earth's surface.
(the maximum seismic-velocity axis; is tilted; about 10 degrees relative to Earth's rotation axis) (it; rotates; T:once)
the maximum seismic-velocity axis it
is tilted rotates
about 10 degrees relative to Earth's rotation axis
T:once