Deep mantle conductivity


  • L. R. Alldredge


Most previous investigators of deep mantle conductivity have assumed that geomagnetic ‘impulses’ containing periods of 2 or 3 years come from the core of the earth. In a recently published paper this author has shown that these impulses can be explained as coming from sources external to the earth. Furthermore, it can be shown that geomagnetic variations with periods near 15 years which traverse the mantle are nearly an order of magnitude smaller than variations with periods near 25 years. These new results permit the derivation of new deep mantle conductivity profiles. When these are matched to the upper mantle conductivity profiles of Banks (1969) at a depth of 1000 km, one obtains a conductivity at the core-mantle interface of 105 mhos/m. This is nearly 3 orders of magnitude greater than that derived by most previous investigators.