Estimation of westward drifting rate of non-dipole fields from Holocene geomagnetic secular variation

对琼海两个沉积物岩心进行了近20天的地磁长期变化记录。从记录中推导出以下四种地磁现象。1)在3800yBP前后记录到一次最大的偏东摆动，与Hyodo（1993）的西漂模式一致。2)估计了一个大型非偶极子源的西漂速率为0.14‰/y。(3)在18000 yBP左右出现了一次以大西风摆动为特征的地磁偏移。4)偏移场也表现出顺时针旋转运动，表明非偶极子场在此期间主要向西漂移。中国洱海近10天的地磁长期变化记录没有与琼海记录不同的最大偏东摆动。原位分析表明，在4000 ~ 1700 yBP范围内，以顺时针旋转运动为主。这一事实与Hyodo的非偶极子场向西漂移模型是一致的。缺少偏东摆动可能是由于地核扭曲。长期变化的短周期分量与琼海湖的短周期分量具有较好的相关性。从全球13个地区获得了全新世地磁的长期变化记录。每张唱片都有不同的质量。来自英国、北美和澳大利亚的记录非常可靠，因为从几个岩心获得了重复记录。利用分离法（Itota et al., 1992）对地磁场运动进行了研究，结果表明，3个地点的周期性以1100和2400 y/c为主，总体上以顺时针旋转为主。根据周期估计的向西漂移速率分别为0.32和0.15‰。后者接近从偏东摆动估计的0.14‰/y。

A record of the geomagnetic secular variation for the last about 20 ky was obtained from two sediment cores in Lake Qionghai, China. The following four geomagnetic phenomena were deduced from the record. 1) A maximum easterly swing is recorded around 3800yBP,being consistent with the westward drifting model by Hyodo (1993). 2) A rate of 0.14ﾟ/y is newly estimated for westward drifting of a large non-dipole source. 3) A geomagnetic excursion characterized by a large westerly swing is found around 18000 yBP.4) The excursion fields also show clockwise rotational sense of motion, suggesting that westward drifting of non-dipole fields is dominant during the period.A geomagnetic secular variation record from Lake Erhai, China for the last 10 ky has no maximum easterly swing unlike the record from Lake Qionghai. In place, it shows that clockwise rotational motion is dominant from 4000-1700 yBP.This fact is consistent with Hyodo's model for westward drifting of a nondipole field. The absence of the easterly swing may be due to core-twisting. Short period components of the secular variation are well correlated with those of Lake Qionghai.Geomagnetic secular variation records during Holocene time are obtained from 13 areas in the world. Each record has different quality. The records from Britain, North America, and Australia are highly reliable because replicate records have been obtained from several cores. The geomagnetic field motions investigated by use of separation method (Itota et al., 1992) show that periodicities of 1100 and 2400 y/c are dominant at the three sites, and that clockwise rotations are dominant on the whole. Westward drifting rates estimated from the periodicities are 0.32ﾟ/y and 0.15 ﾟ/y. The latter is close to the rate 0.14ﾟ/y estimated from easterly swings.