PLANET WITHIN A PLANET - ROTATION OF THE INNER-CORE OF EARTH

The time dependence of the orientation of Earth's inner core relative to the mantle was determined using a recently discovered 10-degree til t in the axis of symmetry of the inner core's seismic-velocity anisotr opy. Two methods of analyzing travel-time variations for rays traversi ng the inner core, on the basis of 29 years of data from the Internati onal Seismological Centre (1964-1992), reveal that the inner core appe ars to rotate about 3 degrees per year faster than the mantle. An anom alous variation in inner-core orientation from 1969 to 1973 coincides in time with a sudden change (''jerk'') in the geomagnetic field.