The Main magnetic field alterations and secular variations within the Earth's mantle
© Yaremenko L.N., Mishchenko Yu.P., Shenderovskaya O.Ya.
As a result of synthesis of magnetic field by IGRF coefficients at distances r=4500, 5000 and 5800 km from the Earth's centre anomalies of the Main magnetic field have been detected under the southern part of South America, under the southern part of Africa and at the central region between Africa and Antarctica that are best seen at r=4500 km and are manifested at the Earth's surface in isoline bends. The secular variations observed at the Eath's surface as very large areal foci are subdivided at r=5000 and 4500 km into several foci whose position coincides well at different distances from the Earth's centre and the Zmax values highly increase with depth. These foci of small areas are mainly situated in seismically active regions. After 20-30 years their intensity may change but the whole region with the series of foci exists for centuries.