Abstract：A test site in a seasonally frozen region in Zhangye City，Gansu Province，China is taken to investigate the ground motion features in different seasons. Micro-tremors are measured and analyzed. Undisturbed samples are taken from the site and triaxial dynamic tests are performed in their unfrozen and frozen states in order to obtain the dynamic parameters，such as shear modulus ratio and damping ratio of the soils. The input for the ground motion analysis，such as boundary conditions，seismic records and soil parameters are discussed. Together with the results from previous seismic risk analysis，the parameters are input into a one-dimensional shear beam model so that ground motion parameters are calculated for the site in seasons with and without frozen layer. Furthermore，different depths of the frozen layer are assumed and peak ground motion parameters and response spectra are calculated. Calculation shows that the seasonal existence of frozen layer can restrain the strong motion to some extent，therefore，the frozen layer has positive effect on the site subjected to seismicity，and the effect increases with the increase of frozen depth；at the same time，the predominant period of the ground decreases with the increase of the depth of frozen layer. The results obtained can also be applied to other regions with similar ground conditions.
