Strong Ground Motion Characteristics of the Saturated Loess Site

Significant differences exist in the ground response of saturated and unsaturated deposits to earthquakes, but few relevant studies exist on strong ground motion in saturated loess. We have selected three loess sites that are highly affected by earthquake‐induced liquefaction hazards, analyzed the nonlinear characteristics of the ground motion response of saturated loess sites through extensive field tests, laboratory experiments, and analytical ground motion response calculations, and compared them with the unsaturated site conditions to reveal the special strong ground motion response characteristics of saturated loess sites. The results show that the PGA of surface ground motion in the Guyuan and Minxian sites is significantly reduced compared with the PGA of input ground motion, and the PGA of surface ground motion in the Tianshui site is slightly increased compared with the PGA of input ground motion. The frequency corresponding to the peak of the Fourier spectrum of the two sites in Guyuan and Minxian decreased significantly, and the frequency corresponding to the peak of the Fourier spectrum of ground motion in the Tianshui site increased slightly. Compared with unsaturated loess, the dynamic stiffness of saturated loess decreases, and the dynamic shear modulus ratio and damping ratio change significantly under high dynamic shear strain. These changes lead to a weakened ground vibration response at the surface, especially at high PGA inputs, highlighting the key differences in ground motions between saturated and unsaturated loess sites. In addition, the dominant frequency of surface motion is significantly lower at saturated loess sites, increasing the risk of site damage during earthquakes. These results emphasize the complex interplay between loess saturation and the dynamic response to earthquakes and demonstrate the need for targeted geotechnical assessment and design in earthquake‐prone areas of the Loess Plateau.