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

为了更好地认识1995年小古根—南步地震的“地震灾害带”，本研究旨在分析岩基山地站点和液化基海岸站点的动力特性相互作用，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诱发过程。利用基于有效应力分析方法开发的具有吸收边界的非线性动力分析程序，对1995年在神户港岛记录的小古根-南部地震在32m以下的二维基本地基模型和神户现场地基模型进行了数值计算。总结如下：1。在分析之前，提出了一种消除人工边界反射波的吸收边界条件，并将其引入现有的有效应力分析程序中，最后证明了该方法的有效性。在层状不规则的地基中，液化会使土体刚度迅速降低，并且由于固有频率的扩展，会引起场地加速度-频率响应函数的收缩和非线性。这意味着频率响应函数在站点转移到低通滤波器。水平相邻层间边界面周围的动力特性在刚度差异极大的情况下受到较硬的地基的影响，在刚度相互相似的情况下受到两种地基的影响。地震烈度的增加降低了沿地表岸线液化引起的加速度响应，从而导致不规则层状山址地表加速度响应集中区的形成。虽然这个地震灾害带是基于神户大地与最大加速度5.4m/s^2的神户地震的具体结合而出现的，但由于神户大地几乎存在于日本的沿海城市，因此该地震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