近年來幾次的大地震皆顯示地震基盤的形狀與分佈深度對於地表地震動的特性有很大的影響，因此要瞭解一個區域的地表震動特性，必須要考慮地震基盤和土層的三度空間分佈的狀況。 複雜的土層和地震基盤分佈讓使用嚴密的數學分析地表震動特性在目前仍有很大的困難，而必須訴諸數值分析方法。本研究採用交錯網格有限差分法(staggered-grid finite-difference method)，結合平行運算的技術所發展完成的分析程式FDM3D，進而模擬三維土層在彈性模式下的受震反應。 由分析結果顯示，同一場址受到不同強度的地震作用，會有不同的地震動特性，即表示用弱震的分析結果來預估強震的反應的作法並不適當。另外根據本研究的分析結果再一次的說明地下結構的重要性，而且若想了解某場址的地震動特性必須對該場址鄰近2-3公里範圍內的地震基盤必須要有詳細的了解。 Recent strong earthquakes reveal that characteristics of ground vibration are affected by the shape and depth of the bedrock significantly. To predict the strong ground motions of a region thus require the information regarding the three dimensional distribution of the bedrock and soil layer of that region. Generally, in the prediction of the strong ground motions of a region, the rigorous analytical solution is formidable due to the complexity of the bedrock and soil layer and thus numerical methods are adopted. In this study, we use program FDM3D, which is a staggered-grid finite-difference method in combination with the parallel computing technique, to simulate the ground vibration response of the 3D elastic model. For a site subjected to different sizes of earthquakes, the characteristics of ground vibration are different, indicating that using the result of small earthquake to predict the ground responses of strong earthquakes is not appropriate. This study also found the importance of the underground-structure for predicting the surface ground motions. It is recommended that the distribution of earthquake bedrock should be determined within a distance of 3 km in the vicinity of the desired region.
