現行耐震設計規範中已經針對台北盆地進行了微分區，將台北盆地分為四個分區，每個分區給定相對應的轉角週期，其中轉角週期最長的台北一區轉角週期為1.60秒。但台北盆地土壤深厚，自然振動週期有可能達3秒以上，因此本研究試著分析過去於台北盆地造成災害的重要地震的強震記錄，發現2002年3月31日發生於花蓮外海的地震在盆地基盤最深的蘆洲及五股一帶轉角週期確實達3秒以上。 本研究將過去二十年內影響台北盆地的重要地震分為板塊介面型地震、板塊內部型地震與地殼地震三種類型，針對台北盆地內的各個強震站計算平均正規化反應譜，以平均正規化反應譜推估轉角週期與放大因子，並以轉角週期為依據進行微分區。 分類結果發現，板塊介面型地震的轉角週期明顯較其他兩種類型地震要長，且與場址的土壤厚度有明顯的正相關。過去曾造成台北盆地地震災害的331花蓮地震轉角週期最長超過3秒，但並非所有板塊介面型地震都是如此。若以各個測站的平均正規化反應譜所推估的轉角週期最長只有約2.2秒。本研究以板塊介面型地震進行微分區的結果大致與現行耐震設計規範的分區相同，由此可知轉角週期主要受到板塊介面型地震所控制，且大地震所推估的轉角週期又明顯更長，未來有更多地震資料時可以重新進行分析以得到更可信的結果，更新耐震設計規範以減少地震造成的損害。 Seismic microzonation for Taipei Basin has been included in the latest version of Seismic Design Code for Buildings, Taiwan. It is divided into four zones according to a corner period, and zone 1 has the longest corner period of 1.60 seconds. However, the deepest soil in Taipei Basin is as deep as 700 meters, the natural period may be more than 3 seconds. This study attempts to analyze the strong-motion records in Taipei Basin from major earthquakes which impact Taipei in the past twenty years. I found that at least for an earthquake which was occurred offshore Hualien on March 31, 2002, and at Luzhou and Wugu area, the corner period is more than 3 seconds. This study classified the selected earthquakes into three types: subduction zone interface earthquake, subduction zone intraslab earthquake, and crustal earthquake. I calculate an average normalized response spectrum for each strong-motion station, then estimate the corner period and amplification factor from the average normalized response spectrum. Microzonation map for Taipei Basin is drawn based on the distribution of corner periods. The result shows that the corner period for subduction zone interface earthquake is longer than that of the other two types, and there is positive correlation between corner periods and the natural period of a site. The 331 Hualien earthquake, which has caused hazard in Taipei Basin, has corner period longer than 3 seconds, but not all the subduction zone interface earthquake has a corner period as long as 331 Hualien earthquake. If we use the average normalized response spectrum to estimate a corner period, the longest corner period is only about 2.2 seconds. In this study, the corner periods from the average normalized response spectrum was used to construct a microzonation map for Taipei Basin. The result indicates that microzonation map from subduction zone interface earthquake is similar in pattern with that in the Seismic Design Code for Buildings. It can be seen that the microzonation is mainly controlled by subduction zone interface earthquakes. It can re-analyzed in the future with more earthquake data to obtain more reliable results and to update the Seismic Design Code for Buildings so that hazard may be mitigated.
