47.日本における地磁気全磁力変化の地域差

Geomagnetic total intensities (F) observed simultaneously with, the same type of proton precession magnetometers at nine stations widely scattered over Japan are compared. The observations have been carried out cooperatively by a research group on earthquake prediction in Japan. During a period from July 1 to 31, 1968, the nine magnetometers have been carefully maintained so as to obtain homogeneous; data. These data are analysed in this report. The amplitude and phase of daily variation of the geomagnetic total intensity change considerably from day to day and from place to place. But examination of the data simultaneously observed shows that there are three different modes in the daily variation in the total intensity. We may define, on the basis of the modes thus found, three areas, i.e. the northeastern, central and southwestern parts of Japan. The following conclusions are reached through the present work. Making use of simple differences in hourly mean values during the night-time between the stations, an anomalous local change in the geomagnetic field in most parts of Japan can be detected, if it occurs, with an accuracy of about 3γ in standard deviation. If weighted differences are used, the accuracy can be slightly improved, so that the standard deviation of comparision is estimated as about 2.5γ. The relative weight for a certain combination of stations is empirically determined. The standard deviation for weighted differences between the stations at a distance within 500km is smaller than that for simple differences by 1γ or so except for those under the influence of socalled ""island-effect"".|地震予知研究計画の一環として,地磁気永年変化精密観測のためのプロトン磁力計が各地に設置された.この磁力計を用いて磁気嵐や日変化などの非局地的磁場変化を日本全土についてどの程度除去できるかを調べた.解析に使用した記録は1968年7月の1ケ月間で,この期間地震予知地磁気グループではプロトン磁力計の保守に万全を期した