Continuous Observation of Geomagnetic Total Intensity in Chugoku District (1):—On Secular Variation in Tottori—

概要

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In order to detect anomalous geomagnetic changes related with earthquake occurrences, an observation of geomagnetic total intensity has been carried out at the Tottori Micro-Earthquake Observatory by means of a proton precession magnetometer since 1967. Geomagnetic total intensity is gradually decreasing with almost constant rate (22.5γ/year). By the detailed investigation for the rate of its secular variation, it may be suggested that annual change has slightly been recognized in the rate of monthly mean variation of geomagnetic total intensity. Daily mean values are conventionally used to calculate the difference of geomagnetic total intensity between Tottori and the Kakioka Magnetic Observatory, because they are free from an effect of anomalous local phase lag in the geomagnetic Sq variation of total intensity. On the other hand, D8t correction to daily mean values is made by using the Sugiura's D8t indices in order to remove the effect of magnetic storm disturbances. It can be concluded that the difference of daily mean values shows fairly stable constant value through a month, but is gradually decreasing through a year, and that the relative secular variation of Tottori to Kakioka is estimated to be about 1.5γ/year, of which value is seemed to be normal in Japan as compared with values obtained from the first and second order magnetic surveys made by the Geographical Survey Institute.
日本測地学会の論文