Analysis of locally concentrated strong motions of multi-phased and irregularly layered grounds of the time-dependent frequency response characteristics

为了对1995年日本兵库县南部地震“地震灾害带“有一个基本的、最好的认识，本研究旨在分析岩基山地场地和岩基海岸场地动力学特征的相互影响，以及基于不规则分层与地震烈度相互关系的地震灾害带的形成过程。利用基于有效应力分析方法开发的带吸收边界的非线性动力分析程序，对1995年科比港岛32 m以下的兵库县南部地震的二维基本地面模型和场地地面模型进行了数值计算。在此基础上，提出了消除人工边界反射波的吸收边界条件，并将其引入到已有的有效应力分析程序中，验证了该方法的有效性.在 ...更多信息 在不规则分层地基中，液化会迅速降低土壤刚度，并由于自然频率的扩展而刺激场地处的加速度-频率响应函数的收缩和非线性。这意味着现场的频率响应函数转移到低通滤波器。水平相邻层间边界面附近的动力特性在刚度相差很大的情况下受到更硬的基础的影响，而在刚度相似的情况下受到两种基础的影响.地震烈度的增加降低了沿着海岸地区表层的液化加速度反应，从而在不规则层状山地场地的地表产生了加速度反应的高集中区。虽然这一地震灾害带是基于科比地面和最大加速度5.4 m/s^2的科比地震的特定组合而出现的，但由于日本几乎沿海城市都存在科比地面，因此这一灾害带也会出现在其他城市。少

For the basic and best understading of "the seismic disaster belt " for the 1995 Hyogoken-Nanbu-earthquake, this study aims to analyze the mutual effects of dynamic characteristics of both rock-based mountain sites and liquefaction-based coastal sites, and also the inducing process of the belt based on the mutual relations between irregular layering and seismic intensity. Numerical computation is performed for the 2D basic ground models and site ground models at Kobe for the 1995 Hyogoken-Nanbu earthquake which was recorded at Port Island of Kobe below 32m of ground surface, using the non-linear dynamic analysis program with the absorbing boundaries which is developed based on the effective stress analysis method.The following is the summary :1. In advance of the analysis, an absorbing boundary condition for eliminating reflection waves from artificial boundaries is developed, introduced into the existing program for effective stress analysis, and finally shows the effectiveness.2. In … More irregularly layered grounds, liquefaction rapidly lowers the soil stiffness and stimulates the shrinkage and non-linearity of the acceleration-frequency response function at sites due to the extension of the natural frequency. This means that the frequency response functions at sites transfer to low-pass filters.3. The dynamic characteristics around boundary faces between horizontally adjacent layers are subjected to harder ground for the case of extremely different stiffnesses and to both grounds for the case of mutually similar stiffnesses.4. Increment of seismic intensity lowers the acceleration response due to liquefaction along the coastal area of surface layers and therefore induces high concentrated area of acceleration response at the surface ground of irregularly layered mountain sites. Though this seismic disaster belt appeared based on the specific combination of Kobe ground and Kobe earthquake of the maximum acceleration 5.4m/s^2, the belt will appear also at other cities because Kobe grounds exist at almost coastal cities in Japan. Less