Taking the landslides triggered by the 2008 Wenchuan Earthquake as examples, their dynamic responses with different epicenter distances due to single and combined action with regionality and spatial heterogeneity of the Primary and Secondary waves were simulated by applying the Universal Distinct Element Code software. The results shows that the slope suffered from the combined action between P and S waves appears instability prior to the slope under single action of P wave. With the epicenter distance increasing, the key controlling factor resulting in the slope failure varies from the combined seismic action between P and S waves to the single seismic action of the P wave. As for the formation mechanism of slope instability, coupled action between the vertical and horizontal seismic forces results in the slope dynamic failure with key action varying from the vertical to the horizontal one. Finally, the initial instability originates always at slope shoulder due to the peak ground acceleration amplification effect and the variation trend of the slope mechanical parameters on its fracturing of the seismic action.

Spatial distribution of slope mechanical parameters on its collapsing and sliding due to seismic load is studied by applying rock dynamic triaxial shear test and finite difference numerical simulation. The results show that a difference in elevation is evident in response of slope initial collapsing and sliding triggered by seismic dynamic influence, i.e., initial fracturing always originates in the place of slope shoulder. Secondly, critical failure strain of slope body unit decreases with its buried depth, and double factors that critical failure strain decreases and peak ground acceleration increases in slope shoulder result in its initial fracturing. Thirdly, dynamic shear strength of slope body unit decreases with its buried depth, and double factors that dynamic shear strength decreases and peak ground acceleration increases in slope shoulder lead to its initial fracturing. The above results contribute to revealing key controlling factors and dynamic process of slope collapsing and sliding triggered by seismic load.

Based on field geological survey, engineering geological investigation and other related analysis to the Xiaonanhai Rockfall triggered by the Qianjiang Ms 6.3 Earthquake in 1856, principal characteristics and failure mechanism of the rockfall is elaborated. It is held that its forming process consists of four steps, namely weathering and denudation, shocking and projecting, collapse-slide accumulating and dammed lake formation. It shows that the mass is a result of comprehensive action including seismotectonic moving and field stress, rock mass structure, topography and geomorphology, seismic wave. First of all, rock mass near both Dakuayan and Xiaokuayan which developed three groups tectonic joints forming "X" shape collapsed respectively towards their free faces, about 145deg155deg direction. Secondly, diameters of rock blocks in accumulation body decrease from northwest to southeast along 150deg direction, and it proves indirectly that the direction of rock mass ejecting is along the same direction.