Abstract: In the earthquake precursor observation network of China, geomagnetic and geoelectric observation instruments are usually closely placed. The high frequency interference to geomagnetic observation data with a period of one hour, which is caused by the electromagnetic induction due to the electrifying operation once an hour during geoelectric observation, will make earthquake precursor and other anomalous geophysical information difficult to be distinguished from the geomagnetic data. The characteristics of this interference information were analyzed in this paper. In order to eliminate the interference, the methods of filtering the high frequency interference in frequency domain by Fourier transform and the typical interference waveform correlation were proposed, respectively. Finally, the effectiveness of our methods was proved by applying to the observation data of Mengcheng station of Anhui province. THis method is applicable to many earthquake precursor observation stations in China.

Key words: Geomagnetic interference, Geoelectric observation, Fourier transform, Correlation