CHARACTERISTICS OF LONG TERM VARIATION OF GEOMAGNETIC FIELD IN RECENT YEARS

The F, H and Z component of geomagnetic data observed by some seismostations in recent 30 years, such as Hongshan, Houtuqiao, are analyzed, and the annual rate of Z component is also studied.The results show:ended the yearly ascending tendency, the long term variation of F and Z component showed a turning re-spectively in 1999 and 2000, but recovered a little in some local region in recent two years;with a descending tendency, the H component did not change.The slow down of variations in Z component is usually relevant to the relatively strong earthquake in North China area.