SEISMIC MOTION AMPLIFICATION EFFECT OF SHALLOW-CUTTING HILL-CANYON COMPOSITE TOPOGRAPHY

The hill-canyon composite topography is a common site in Western China. A large number of infrastructures, such as bridges and dams, have been built in such a site. However, field investigations after earthquakes show that surface irregularities may cause seismic motions amplified in such a site. Seismic motion amplification has an adverse effect on the stability of slopes and the safety of buildings. Therefore, it is significant to investigate the seismic motion amplification effect of hill-canyon composite topography. In this paper, we focused on the seismic response of the shallow-cutting hill-canyon composite topography. In such a site, the relative height between the hill top and the base of canyon always ranges from 100 m to 500 m. Employing the boundary integral equation method, the seismic motion at every interesting position in such a site was obtained. Then, parametric studies were conducted, including the effects of the types of waves(P and SV waves), the frequencies of incident waves, the angles of incidence, and the geometry characteristics of the hills and canyons on the seismic motion amplification effect of hill-canyon composite topography. The results show that the existence of the hills clearly changes the spatial distribution of seismic motions. The surface seismic motion is either amplified or de-amplified, depending on the frequency of incident wave. Different types of waves determine different spatial distribution patterns of seismic motions. The influence of the depth of the canyon on amplification pattern depends on the types of waves. The geometric asymmetry contributes to the asymmetry of the spatial distribution of seismic motions. The asymmetry is much clearer in the case of SV wave incidence than that in the case of P wave incidence. In the case of oblique incidence, seismic motions near the slope facing away from the source are much larger than those near the slope facing towards the source in the canyon. The method in this paper is efficient to investigate the seismic motion amplification effect of hill-canyon composite topography, and capable to obtain the seismic motion at every position, which will be used in the stability analysis of slopes.