基岩地形对地震动影响研究

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。

Effect of bedrock terrain on seismic ground motion

Based on theoretical analysis, the spectral element method is used to study the effect of bedrock terrain on ground motion. The achievements are as follows: (1) The intensity of bedrock ground motion is related to bedrock occurrence, incident orientation of seismic wave and other factors. The incident orientation of seismic waves is closer to the tangent direction of bedrock surface, and the intensity is smaller. On the contrary, the incident orientation is closer to the normal direction of bedrock surface, and the intensity is stronger. (2) The presence of bedrock with convex terrain leads to weakening of the surface intensity of ground motion, and thus to the formation of the relative weakening zone of ground motion intensity. While, the presence of bedrock with concave terrain leads to strengthening of the surface intensity of ground motion, and thus to the formation of the relative enhancement zone of ground motion intensity. (3) Under different bedrock topographic dips, there are different relative variation zones of ground motion intensity. Under the action of the bedrock with convex terrain, the relative weakening zone of ground motion intensity is 1.13~1.69 times larger than the bedrock convex area, which increases gradually with the increase of bedrock topographic dip. Whereas, under the action of the bedrock with concave terrain, the relative enhancement zone of ground motion intensity is 0.5~1 times smaller than the bedrock concave area, which decreases gradually with the increase of bedrock topographic dip. (4) Under different cover layer thicknesses, there are different relative variation zones of ground motion intensity. Under the action of the bedrock with convex terrain, the ratio of the relative weakening zone ground motion intensity to the bedrock convex area increases gradually with the increase of cover layer thickness. However, under the action of the bedrock with concave terrain, the ratio of the relative enhancement zone of ground motion intensity to the bedrock concave area decreases gradually with the increase of cover layer thickness.