| Research Abstract |
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
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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
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