利用地磁场综合模型CM4分析中国大陆地区地磁场变化

第四代地磁场综合模型CM4是迄今为止将地磁场的内源场和外源场分离得最为彻底的数学模型.利用该模型结合Taylor多项式模型,基于1960—2000年期间中国大陆地区的实测数据,计算并分析了以10a为间隔的内源场和外源场的变化情况,通过将1960—1990年的所有磁异常点归算至2000年以分析地壳磁异常场的总体分布趋势.结果显示:地磁北向分量X的内源场强度总体呈逐年减弱的趋势,从1960年到2000年共下降了约750nT,外源场强度总体呈先增强后减弱的趋势,共下降了约32nT;地磁东向分量Y的内源场强度总体呈先减弱后增强的趋势,1960—2000年期间共上升了约40nT,外源场强度总体呈先减弱后增强再减弱的趋势,共上升了约3.8nT;地磁垂直分量Z的内源场变化趋势与Y分量类似,共上升了约600nT,外源场总体呈先减弱后增强的趋势,共上升了约4.6nT.对于地壳磁异常场,X分量、Z分量、地磁总强度F和地磁水平分量H在中国大陆地区都为负异常分布,X分量和H分量的负异常强度随经度增加而减弱,Z分量和F分量则相反;Y分量和磁偏角D的分布较为类似,在中国的中西部大部分地区为正异常,强度随经度增加而减弱,磁倾角I主要以负异常为主,负异常强度随经度增加而增强.

Analysis of variation in geomagnetic field of Chinese mainland based on comprehensive model CM4

The fourth generation of comprehensive model of geomagnetic field CM4 is a numerical model in which earths magnetic field can completely be divided into internal and external parts. In this paper we have calculated and plotted the grid values of internal and external fields of Chinese mainland in every 10 a from 1960 to 2000 by combining CM4 with Taylor polynomial model based on all survey data during 1960—2000, and made more efforts to analyze the whole distribution of crustal anomaly field. Results show that internal field value of northern component X decreased with time. The amplitude was about 750 nT in the period from 1960 to 2000, the trend of external field variation increased in 1960, then gradually decreased about 32 nT until 2000. The internal field value of eastern component Y decreased first, then continuously increased, and its intensities decreased about 40 nT from 1960 to 2000. The trend of external field variation was increased, decreased and increased as time went on, and the external field increased up to about 3.8 nT since 1960. The internal field value of vertical component Z was similar to that of Y, its intensities totally increased about 600 nT. The trend of external field variation decreased and then increased with time, amplitude of which was about 4.6 nT. As for anomalous field, the distributions of components X and Z, total intensity F, and horizontal component H were all negative, the intensities of X and H decreased with longitude while those of Z and F increased. The distributions of Y and declination D were very similar and both of them had positive values in west-central region of China. Their intensities decreased with longitude. The distribution of inclination I was mainly negative, and its intensity increased with longitude.