Anomalous Secular Variation of Geomagnetic Total Intensity In Chugoku District, Japan

Abstract

In 1971 Geomagnetic surveys in the Chugoku district have been carried out by using a portable proton precession magnetometer. The ordinary method of epoch reduction to eliminate non-local changes in the geomagnetic field has been slightly modified by using the data obtained at the Tottori Micro-Earthquake Observatory, where an observation of geomagnetic total intensity has been carried out since 1967 by means of a proton precession magnetometer. Secular variations of geomagnetic total intensity during a period from 1965 to 1971 at various stations were examined comparing the available data obtained by the Geographical Survey Institute during the period from 1965 to 1966. The results show that there may exsist marked anomalous secular variations in the Chugoku district, whose features are fairly systematic. Some correlation between the areas having the anomalous secular variation and the geomagnetic anomalous regions has been recognized. This suggests that the anomalous secular variation in the Chugoku district may be caused by the piezomagnetic effect or the crustal movements due to the horizontal compression of E-W trend in Southwest Japan.