Variation of Geomagnetic Vector in 10^5 to 10^6 Years

1.基于冰岛样品的磁场矢量变化研究我们测量了冰岛北部Storutjarnir附近两个垂直层序(LT和SI)中约150个熔岩流的古地磁方向。在这些流动中获得了大约20个样品的K-Ar年龄。结果表明，这些熔岩的喷发时间为2~3 Ma。我们从已发表的资料中收集了古地磁和年龄数据，形成了一个包含约6000个熔岩信息的数据库。该数据库的一些分析结果将在1996.2年3月的学会会议上提出。古强度数据库的建立和统计分析。我们通过汇编已发表的材料，形成了古强度数据库，并向公众开放。我们对这些数据进行了统计处理，以了解磁场强度的变化特征(田中、内村和河野，地球物理，国际学报，120，97,1995)。一种新的古分子变化模型(PSV)我们发展了一种新的PSV模型，其基础是假设在足够长的时间内，地磁场的高斯系数可以被视为独立的随机变量。Kono和Tanaka(J.Geomag.GeoElectrtr.，47,115,1995)将这种分析应用于虚拟地磁极(VGP)的散射，而Kono和Hiroi(Earth Planet.Science Lett，出版社，1996)使用相同的方法分析古强度数据。结果表明，g^1(ORH^1)比其他非偶极子项大得多，非偶极项随谐振度呈指数递减。

1. Study of vector variation of the magnetic field based on Icelandic samples.We measured the paleomagnetic directions of about 150 lava flows from two vertical sequences (LT and SI) collected near Storutjarnir, northern Iceland. K-Ar ages were obtained for about 20 samples in these flows. The results indicate that these lavas erupted in the time interval of 2 to 3 Ma ago. We collected paleomagnetic and age date from published materials and formed a database containing the information of about 6000 lavas. Some results of analysis of the database will be presented at the society meeting in March 1996.2. Formation of paleointensity database and statistical analysis.We formed a paleointensity database by compiling published materials, and made it open to the public. We have done some statistical treatment of these data to see the characteristics of variation of magnetic field intensity (Tanaka, Uchimura, and Kono, Geophys.J.Int., 120,97,1995).3. A new model of paleosecular variation (PSV)We developed a new model of PSV based on the assumption that the Gauss coefficients of the geomagnetic field can be treated as independent random variables in sufficiently long time. Kono and Tanaka (J.Geomag.Geoelectr., 47,115,1995) applied this analysis to the scatter of virtual geomagnetic poles (VGPs), while Kono and Hiroi (Earth Planet.Sci.Lett., in press, 1996) used the same method to analyze the paleointensity data. Results indicate that g^1_) (orh^1_) is much larger than other nondipole terms which decrease exponentially with the degree of the harmonic.