采用有限元离散模型、黏弹性人工边界和中心差分积分格式相结合的方法，开展三维凹陷地形场地地震反应计算，分析了P波和SV波入射下均匀弹性半空间三维棱锥形凹陷、半球凹陷和棱柱形凹陷地形场地对场地地震动的影响特征与差异。研究表明：（1）不同形状的凹陷地形对场地地震动的影响差异显著，即棱柱凹陷地形>半球凹陷地形>棱锥凹陷地形，但不同形状凹陷地形影响之间的差异更多地表现在中频范围内；（2）凹陷地形对地震波具有复杂的散射作用，无论是垂直入射的P波还是垂直入射的SV波（仅竖向或水平向地震动输入），在凹陷区及附近均能产生两个方向很显著的地震动，且在SV波垂直入射下的凹陷散射更为强烈，其产生的竖向地震动幅值甚至超过水平向的；（3）凹陷地形可能会产生地震动的地形边缘效应，棱柱形凹陷边缘处地震动被显著地放大，而半球凹陷地形、棱锥形凹陷地形中这一效应相对较弱。研究揭示了凹陷边缘陡峭程度对场地地震动有显著的影响，而且凹陷地形边缘效应可能存在并与凹陷边缘陡峭程度密切相关。这一研究结果对实际工程问题分析给出了重要提示：建立凹陷地形的简化分析模型时需要特别关注凹陷边缘部位的合理处理。研究结果可应用于山区工程建设，特别是桥梁和水坝建设，为其抗震设防考虑不同凹陷形状地形对场地地震动影响的特征及差异，特别是可能出现的地形边缘效应提供参考。The seismic responses of three-dimensional (3D)concave topography sites were calculated by the combination method of finiteelement discrete model

the viscoelastic artificial boundary and the centraldifference integral formula

and the characteristics and differences of theinfluence of pyramid-shaped

hemisphere-shaped and prism-shaped concavetopographies in homogeneous elastic half space on site ground motion wereanalyzed under the vertical incidence of P wave and SV waves. (1) The influenceof different shapes of concave topographies on site ground motion issignificantly different

namely

the prism-shaped concave topography>thehemisphere-shaped concave topography>the pyramid-shaped concave topography

but the differences between the different concave topographies are moremanifested in the medium frequency range. (2) Concave topographies have acomplex scattering effects on seismic waves. Whether it is vertically incidentP wave or vertically incident SV wave (only vertical or horizontal seismicmotion input)

it can produce significant ground motions in both directions inand near the sag area

and while SV wave is vertically incident

the wavescattering of concave topography is more intense

and furthermore the amplitudeof ground motion in vertical direction generated by SV wave is even greaterthan that in horizontal direction. (3) The concave topography may cause thetopographical edge effect of ground motion

and the ground motion at the edgeof prism-shaped concave is significantly amplified

while this effect isrelatively weak in the pyramid-shaped and hemisphere-shaped concavetopographies. The study reveals that the steep degree of the concave edge has asignificant impact on site ground motion

and that the edge effect of concavetopography may exist and is closely related to the steep degree of the concaveedge. This research result gives an important hint for the analysis ofpractical engineering problems

that is

the rational treatment of concave edgeparts should be paid special attention to when establishing a simplifiedanalysis model of concave topography. The research results can be applied tothe engineering construction in mountainous areas

especially bridge and damconstruction

and provide a reference for its seismic fortification to considerthe characteristics and differences of different shapes of concaves on siteground motion

especially the possible topography edge effect.