Establishment of archeomagnetic secular variation curve in pre-historic age

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As the accumuliation of archeomagnetic data, precise archeomagnetic secular variation curves of the Hokuriku and Tokai Districts are established for the historic age. On the contrary, for the Japanese pre-historic age before Kofun Period, we have very insufficient amount of archeomaghetic data to trace back the variation of the geomagnetic field precisely.The main aim of the present research project is to collect archeomagnetic data of pre-historic age as many as possible. Another fact, which makes difficult in establishing the pre-historic secular variation curve, is the regional anomaly of the geomagnetic field in and around Japanese Islands. Archeomagnetic data, therefore, should be obtained from sites of widely spreading all over the islands and the vicinity.To cover the wide area and long period, archeomagnetic data are obtained from Aomori prefecture (Sannaimaruyama Site, Shinmachino Site) , Tochigi prefecture (Shitomaki Site) , Shizuoka prefecture (Surugayama Site), Toyama prefecture (Hanakiri Site), and Korea (Chunshan-dong Site, Wau-ri Site, Dujeong-dong Site, Daepyeong-ri Site, Paldal-dong Site, , Neuk-do Site). Ages of those sites are ranging from Jomon Period to Early Kofun Period.As the results of above-mentioned sampling and measurements, the outline of archeo-secular variation in Korea is obtained for the period from the 2nd century to 18th century A.D. The most conspicuous aspect obtained from this study is that the Korean geomagnetic declination between the 2nd and 4th century deviates more than 10 degree eastward as compared with that of Japanese one of same age. The regional gradient of the geomagnetic -field at the time seems to be much grater than that of the present.