基于四川盆地及台北盆地震害分布的差异,将虚拟激励法与有限单元法结合,应用于场地的随机地震反应分析中。将沉积盆地截面简化成等腰梯形,建立二维平面应变模型,通过数值试验,研究了沉积盆地场地的地震反应,探讨了盆地效应的影响参数。主要结论如下:①由于地震波在盆地边缘的反射效应,盆地场地表面的地震反应较成层场地有较大的改变,水平加速度标准差可提高150%;场地边缘附近的竖直加速度标准差与水平加速度标准差量级相当;②当盆地宽度较大时,盆地边缘仅对场地边缘附近的地震反应有较大影响,影响范围大概为l倍(以水平加速度标准差为评价标准)或者3倍(以竖直加速度标准差为评价标准)盆地边缘倾斜基岩面的水平投影长度;③随着盆地深度的增加,瓮地场地表面的最大水平及竖直加速度标准差增加;④随着土层剪切波速的增加,盈地场地表面的最大水平加速度标准差几乎不变,但最大竖直加速度标准差减小。
The spatial distributions of disasters in Taipei Basin and Sichuan Basin are different. A series of two-dimensional plane strain models for sedimentary basins, the cross sections of which are simplified to isosceles trapezium, are established to analyze the seismic response of sedimentary basins and to study the major influencing parameters of basin effect. It is concluded that because of the reflection of seismic waves at the boundary of basins, contrasted to horizontal layered sites, the seismic response of basin sites makes a large difference. The standard deviation of horizontal acceleration may rise by 150%, and the standard deviation of vertical acceleration is corresponding to that of horizontal acceleration in magnitude. If the size of basins is relatively large, the basin effect just has a relatively distinct impact on the seismic response of the edge of basins, and the incidence is approximately equal to the projected length of the inclined bedrock surface at the edge of basins, concluded by the standard deviation of horizontal acceleration, or triple of that, concluded by the standard deviation of vertical acceleration. The maximum standard deviation of acceleration increases with the increase of the depth of basin sites. The maximum standard deviation of horizontal acceleration remains virtually unchanged and that of vertical acceleration reduces with the increase of shear wave velocity of soil.