SV波斜入射作用下梯形沉积河谷场地地震动分析

Seismic motion analysis of a trapezoidal sedimentary valley subjected to obliquely incident SV waves

河谷场地地震动分布特征研究对高坝等跨河谷工程的抗震设计具有重要意义。采用无限元人工边界结合等效荷载输入方法,数值分析了梯形沉积河谷的几何参数和地震波入射角对加速度放大系数分布特征的影响。结果表明:坡度较小河谷的加速度放大系数极大值位置位于河谷中部和两侧,随着坡度增大,加速度放大系数极大值位置逐渐远离河谷两侧,进而向河谷中部距地表一定深度处转移;对于窄河谷,河谷两侧影响区域重叠,导致地震异常剧烈,地表加速度放大系数远大于宽河谷情况;随着地震波入射角增大,加速度放大系数最大值位置由河谷中部往迎波侧移动,河谷地形效应不断增强,迎波侧聚焦放大、背波侧滤波减小现象越明显。

Investigating the distribution characteristics of seismic motion in valley sites is crucial for the seismic design of cross-valley projects,such as high dams.The analysis of the impact of geometric parameters of trapezoidal sedimentary valleys and the angle of seismic wave incidence on the distribution characteristics of the acceleration amplification coefficient was conducted using the infinite element artificial boundary and the equivalent load input method.The results show that the valley sites with a low slope exhibit maximum values of acceleration amplification coefficients in the middle and on both sides of the valley.As the slope of valley increases,these maximum values of acceleration amplification coefficients gradually shift away from both sides of the valley and concentrate towards the middle of the valley at a certain depth below the surface.In narrow valleys,there are overlapping influence areas on both sides,resulting in abnormal and intense seismicity,characterized by significantly higher surface acceleration amplification coefficients compared to wider valleys.Moreover,with an increase in the incident angle of seismic waves,the maximum acceleration amplification coefficient shifts from the middle of the valley towards the onshore side,intensifying the topographic effect of the valley.This leads to a pronounced phenomenon of focusing and amplification on the onshore side,while reducing the filtering effect on the opposite side.