Establishment of archeomagnetic secular variation curve in pre-historic age

随着考古地磁资料的积累，建立了北海和东海地区历史年代的精确考古地磁长期变化曲线。相反，对于高峰期之前的日本史前时代，我们缺乏大量的考古地磁资料来准确追踪地磁场的变化。本研究的主要目的是尽可能多地收集史前时代的考古地磁数据。另一个给建立史前长期变化曲线带来困难的事实是日本群岛及其周边地区的地磁场区域异常。因此，考古地磁数据应从广泛分布在岛屿及其附近的地点获得。为了覆盖大范围和长时间，考古地磁数据从青森县(Sannaimaruyama站点、新町站点)、Tochigi县(Shitomaki站点)、静冈县(Surugayama站点)、富山县(Hanakiri站点)和韩国(春山洞站点、Wau-ri站点、都正洞站点、大平里站点、Paltalong站点、Neuk-do站点)获得。这些遗址的年代从柔门期到高峰期早期不等。作为上述采样和测量的结果，获得了公元2世纪至公元18世纪韩国的古长期变化轮廓。本研究得到的最显著的方面是，2世纪至4世纪的朝鲜地磁偏角与日本同时代的地磁偏角东移10度以上。当时地磁场的区域梯度似乎比现在大得多。

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.