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在理论分析基础上,采用谱元法研究了基岩地形变化对地震动的影响。结果表明:1基岩面上地震动强度大小与基岩面的产状、地震波入射方向等因素相关。地震波入射方向越接近基岩面切线方向,基岩面上地震动强度越小;越接近基岩面法线方向,则越大。2基岩凸起地形的存在,导致与凸起区相对应地表处的地震动强度减弱,形成地震动强度相对减弱区;基岩凹陷地形的存在,导致与凹陷区域相对应地表处的地震动强度增强,形成地震动强度相对增强区。3基岩地形陡度不同,地震动强度相对变化区不同。基岩凸起地形作用下,地震动强度相对减弱区是基岩凸起区的1.13~1.69倍,具有随陡度增大而逐渐增大的趋势;基岩凹陷地形作用下,地震动强度相对增强区是基岩凹陷区的0.5~1倍,具有随陡度增大而逐渐减小的趋势。4覆盖层厚度不同,地震动强度相对变化区也不同。基岩凸起地形作用下,地震动强度相对减弱区与基岩凸起区的比值具有随覆盖层厚度增大而逐渐增大的趋势;基岩凹陷地形作用下,地震动强度相对增强区与基岩凹陷区的比值具有随覆盖层厚度增大而逐渐减小的趋势。
Based on the theoretical analysis, the influence of the bedrock topography on the ground motion is studied by the method of the spectrum element method. The results show that: 1 The intensity of ground motion on bedrock surface is related to the occurrence of bedrock surface and the direction of seismic wave incident. The closer the seismic wave incident direction is to the tangential direction of bedrock, the less earthquake intensity on the bedrock surface. The closer to the normal direction of bedrock, the larger is. 2 The existence of the topography of the bedrock causes the ground motion intensity at the surface corresponding to the raised area to weaken, resulting in a relatively weakened area of ground motion intensity. The presence of the depressed topography of the bedrock causes the ground motion corresponding to the depressed area Intensify the intensity, the formation of relatively strong earthquake intensity area. 3 The bedrock topography has different steepness, and the relative change range of earthquake intensity is different. Under the action of bedrock raised terrain, the relative weakening area of ground motion intensity is 1.13-1.69 times of the raised area of bedrock, and tends to increase with the increase of steepness. Under the action of bedrock depression terrain, The area of enhancement is 0.5 ~ 1 times of the depression area of bedrock, and has the tendency to decrease gradually with the increase of steepness. 4 The thickness of cover is different, and the relative change of earthquake intensity is also different. Under the action of bedrock topography, the ratio of ground weakening area to basement hillock area tends to increase with the increase of cover thickness. Under the action of bedrock depression topography, the relative increase of ground motion strength and The ratio of bedrock depression area tends to decrease gradually with the increase of cover thickness.