REGIONAL DIFFERENCES OF ARCHEOMAGNETIC FIELD AND THEIR APPLICATION TO THE ARCHEOMAGNETIC AGE DATING

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As the archeomagnetic data have been accumulated, it is revealed that there are considerable regional differences in the ancient geomagnetic field within the islands of Japan. The differences are so big that ages obtained by the archeomagnetic dating show errors more than 100 years in the certain period.The aim of the present research is to clalify the regional differences and to establish the standard archeo-secular variation curve for each region in Japan to contribute to the more acculate archeomagnetic age dating.The present research project allowed us accomplishing the standard archeo-secular variation curves for the Hokuriku District and also for the Tokai District. The archeo-secular variation curve for the formar (Hokuriku District) is obtained for a period from 500 A.D.to 1550 A.D.and that for the latter (Tokai District) is for a period of 900-1700 A.D.We obtained archeomagnetic data from the Hokkaido and the Aomori Prefectures where scarce archeomagnetic results are reported. Moreover, we succeeded to obtain archeomagnetic data from Korea. Those will play a very important role to consider and clarify the distribution of the archeomagnetic field and its secular variation in the east Asia.Archeomagnetic measurements were carried out on charcoal kilns which had a close connection with the iron production industry in the ancient times in Hokuriku District. This study revealed that the iron production industies were prosperous not only in the Nara-Heian and the Bakumatsu (the end of Edo Era)-Meiji periods but also in the 12-13th Centuries in the Hokuriku region.