Secular Variation of the Geomagnetic Total Force during the Last 5000 Years

Abstract

Intensities of the geomagnetic total force (F) at various epochs during the last 5000 years are deduced from the intensity of natural remanent magnetization of basaltic lavas and baked potteries of known ages. Results show that F increased between about 5000 years ago and 2000 years ago when F reached its maximum value, being about 1.5 times as large as at present; F then decreased gradually until the present time. The results are probably accompanied by regional secular variation of appreciable magnitude.