佘山地震监测中心站地磁观测百余年资料的跟踪分析

Tracking and analysis of geomagnetic observation data for over a hundred years at the Sheshan Earthquake Monitoring Center Station

选用佘山地震监测中心站1874-2005年地磁七要素D、H、Z、X、Y、F、I年均值数据,利用一阶差分方法,计算各地磁要素差分值ΔD、ΔH、ΔZ、ΔX、ΔY、ΔF、ΔI,并绘制差分值趋势变化图,统计地磁七要素年均值数据在百余年观测历程中异常台阶出现的年份、变化方向及幅值大小;同时,利用地磁环境变化定量模型,计算地磁异常场模量ΔT,统计分析佘山台百余年来地磁观测的场地环境指标。研究得出以下结论:①磁偏角D在长趋势变化中出现2次较为明显的台阶下降变化,其中1908-1910年变化-42.47′,1965年变化-41.76′,其他时段变化较平稳。②磁倾角I在1893-1895年呈向下变化,变化量-45.62′,其在1991年呈反向向上变化,变化量44.61′。③佘山地区磁场总强度F、水平强度H、垂直强度Z具有明显的周期性变化特征,应与太阳活动周期效应有关。F、H、Z的长期变化趋势较为相同,在1884—1887年均存在一个大幅度台阶,变化幅度均在600 nT以上。④在地磁环境变化定量计算与分析中,发现1908年、1933年ΔT>100 nT,显示明显受到观测环境的较大影响。查找史料发现,应为1908年上海徐家汇有轨电车建设运营和1933年沪宁铁路建设台站迁移至佘山,观测环境不稳定所致。

Using annual mean data of seven geomagnetic elements D,H,Z,X,Y,F,and I from 1874 to 2005 at the Sheshan Earthquake Monitoring Center Station,the first-order difference method is used to calculate the difference values of magnetic elementsΔD,ΔH,ΔZ,ΔX,ΔY,ΔF,andΔI in various regions.We then draw a trend chart of differential values and calculate the year,direction,and amplitude of abnormal steps in the annual mean data of the seven geomagnetic elements over a hundred years of observation.At the same time,we use a quantitative model of geomagnetic environmental changes to calculate the modulus of the geomagnetic anomaly fieldΔT and carry out a statistical analysis of the environmental indicators of the geomagnetic observation site at Sheshan Observatory over the past century.The following conclusions can be drawn from the results:①The magnetic declination angle D shows two significant step-down changes in the long-term trend,with a change of-42.47′from 1908-1910 and a change of-41.76′from 1965.The changes in other periods are relatively stable.②The magnetic dip I changed downwards from 1893 to 1895 with a change of-45.62′,and it changed inversely upwards in 1991 with a change of 44.61′.③The total magnetic field intensity F,horizontal intensity H,and vertical intensity Z in the Sheshan area have obvious periodic changes,which should be related to the periodic effect of solar activity.The long-term trends of F,H,and Z are relatively similar,with a significant step from 1884 to 1887,with changes above 600 nT.④In quantitative calculation and analysis of geomagnetic environmental changes,it was found that in 1908 and 1933ΔT>100 nT,indicating significant influence from the observed environment.By looking up historical materials,it was found that the unstable observation environment was caused by the construction and operation of the Xujiahui tram in Shanghai in 1908 and the relocation of the Shanghai Nanjing Railway construction station to Sheshan in 1933.