Amplification of thickness and Stratigraphy of loess deposit on seismic ground motion in the Yellow River Basin

The widely distributed loess deposits in the Yellow River Basin exhibit unique engineering geological characteristics. The variations in their thickness and stratigraphic structure significantly amplify ground motion parameters, directly influencing the regional seismic hazard risk level. This study methodically conducted on-site studies and observations of building collapses and damages resulting from seismic amplification effects, using the Wenchuan M_S8.0 earthquake as a case study. Comprehensive experimental and numerical simulation studies were carried out. A large-scale shaking table test was performed, and numerical models for 14 different loess sites types were established. Various types of seismic waves were incorporated into these models for systematic numerical simulation calculations. The research reveals the mechanisms by which loess deposit thickness and stratigraphic structure in the Yellow River Basin affect seismic ground motion amplification. The results indicate that as the epicentral distance increases, the peak ground motion shows a marked attenuation trend, with the horizontal component attenuating substantially faster than the vertical component. As the overlying loess layer thickness increases from 50m to 100m, the seismic intensity may escalate by 3-4 degrees, and the peak acceleration may amplify by 1.5−2.2 times. With the augmentation of loess deposit thickness and the proliferation of soil layers, both the peak acceleration response spectrum and the characteristic period demonstrate an upward tendency, exhibiting slight fluctuations contingent upon the seismic wave type.