UCLA

Calculations of electromagnetic torques between the fluid outer core and the heterogeneous lower mantle demonstrate that the geomagnetic field can lock with the mantle during polarity transitions. We show that the Virtual Geomagnetic Pole (VGP) is attracted toward mantle regions with low electrical conductivity and repelled from mantle regions with high conductivity. Using seismically-determined structure of the lower mantle to infer the pattern of conductivity variations at the base of the mantle, we find two preferred reversal routes for the VGP, one beneath the Americas and another beneath Asia. These paths, particularly the one beneath the Americas, lie close to the VGP paths seen in some sedimentary and lava records of polarity reversals, suggesting that the core and mantle are electromagnetically coupled during reversals. Copyright 1996 by the American Geophysical Union.