Abstract：Based on microseism tests at the typical permafrost sites along the Qinghai—Tibet Railway，the characteristics of frequency spectra of the permafrost sites are determined. The changes of the predominant frequencies with ground temperatures and permafrost tables，and the differences in frequency spectra between permafrost sites and loess sites are analyzed. Statistical curves of frequency spectra by Fourier analysis at these typical permafrost sites in the plateau are the shapes with single dominant peak value. The predominant frequencies of microseism¢s vertical components are between 3.3 Hz and 4.8 Hz；and the horizontal predominant frequencies are between 2.3 Hz and 4.7 Hz. The microseism is a macroreaction of lithologic characteristics，especially physico-mechanical features of those shallow strata，which depends on the strength of permafrost sites；and it will be changed with the ground temperatures and permafrost tables. Analytical results show that the predominant frequencies of microseism¢s vertical components are correlated with ground temperatures and permafrost tables at the permafrost sites：the higher the ground temperature is，the lower the vertical predominant frequency is；the higher the permafrost table is，the greater the vertical predominant frequency is. It indicates that there is a close relation between predominant frequencies and the strengths of permafrost sites. Moreover，a comparative result of microseism¢s predominant frequencies in permafrost sites and loess sites reveals that there is an obvious difference in predominant frequencies of microseism between the two different areas：the ranges of predominant frequencies at the permafrost sites are narrower than those of the loess sites；and there is a higher value of predominant frequency of microseism in the permafrost sites.
