Based on the microtremor observation data of 539 measuring points in Tianshui

horizontal-to-vertical spectral ratio and the predominant frequency are analyzed. According to the geological records of 59 boreholes and shear wave velocity distribution

two methods including the quarter-wave length and statistical relationship between overburden thickness and predominant frequency are applied to inverse the overburden thickness. The results show that the quarter-wave length has great flexibility to the third and the fourth terraces with a thicker overburden and single stratum; high accurate formula simplifying the influence of shear wave velocity is drawn with the method of the statistical relationship between the overburden thickness and the predominant frequency; and it is suitable for the whole studied area.