Characteristics of geomagnetic storm spectra in middle and low latitude regions and their relation with the tangshan earthquake

The characteristics of 80 geomagnetic storm spectra have been analyzed and compared for the records at seven observatories: Beijing, Qingguang, Changli, Guangzhou, Sheshan, Wuchang and Changchun during 1973–1977. The general natures of the spectra are thus obtained. The results are as follows. First, there are synchronous trends of change in the magnetic storm spectral amplitude at the seven observatories. Second, the sepctral slopes of all the magnetic storms are almost the same. The yearly average values of the spectral slopeb are quite steady within the period range from 0.5 to 6.8 hours. This means that the magnetic storms have the same energy partitioning factor. Third, there are significant changes in the yearly average values of spectral interceptsa for the three observatories of Beijing, Qingguang and Changli which are near the Tangshan earthquake area, but the values are quite steady for the four observatories of Guangzhou, Sheshan, Wuchang and Changchun which are far from the earthquake area. It seems that the noticeable changes are related to the great Tangshan earthquake of July 28, 1976.