中国四川地区地球磁场强度的长期变化

SECULAR VARIATION OF GEOMAGNETIC INTENSITY IN THE SICHUAN REGION,SW CHINA

运用 Thellier 逐步热退磁法,主要测定了我国四川一些地区新石器时期至明、清各朝代的地球磁场总强度值。本文结果表明,在过去5000多年里,该地区地球磁场的总强度随时间呈较大幅度的变化。将该地区与我国其它相关地区地球磁场总强度的长期变化曲线进行对比研究的结果表明:变化的总趋势大致可比,但最高值出现的时间不同.从过去四千年间,新疆、四川、广东、福建及洛阳一些地区的地球磁场强度变化曲线中最高峰和跨时千余年的"M"型变化中低峰出现的时间推得的滞后速度在0.01°—0.03°/a 之间。

Geomagnetic field intensity has been determined for the last 5000 years by using the Thellier method of stepwise thermal demagnetization with about 185 archeological samples (potsherds,bricks,baked clays ets.) from Sichuan,Yunnan and Guizhou provinces.Results show a large fluctuation.The highest value of the geomagnetic intensity for the last 5000 years from various regions was appeared with lag from the east to the west;at the same time some features such as a maximum with double peaks spanning about a thousand years were appeared at the time with lag from the west to the east The rate of lag is 0.01°—0.03°/a.It is clear that characteristics of the secular variation of the geomagnetic intensity in China determined from systematic archaeomagnetic study are influenced by local features of the non-dipole field in a considerable extent.