應用地震震波特徵建構台北盆地地震災害潛勢模式

Abstract

本研究採用地理資訊系統（Geographic Information Systems，GIS）和單站頻譜比（Horizontal-to-Vertical Spectral Ratio，HVSR）等技術，分析了台北盆地歷年來的強震資料，並獲得頻譜比值(H/V)和主頻值(DF)等地震參數（變數）。隨後，利用社會科學統計SPSS軟體，進行多變量迴歸分析，針對代表峰值加速度（PGA）的地震動強度，建立了一個模型方程式，以瞭解各個變數對場址PGA的影響程度。根據國家地震工程研究中心研究成果得知，主頻分佈主要與底下的沖積層相關，而台北盆地的場址效應與松山層密切相關。除了沖積層厚度外，沖積層的剪力波波速(Vs30)，也對主頻大小產生影響。在相同沖積層厚度中，礫岩堆積相較於砂礫堆積，具有較高的主頻。故挑選主頻時Vs30必為參考值之一。 另外，土壤液化潛能敏感性，亦是地震災害潛勢因素之一。根據Nakamura（1996）的研究，土壤液化潛能評估值Kg可以通過公式Kg=Ag²/Fg計算得出。其中，Ag代表主頻放大倍率，即H/V ratio值，而Fg則表示為主頻（Dominant Frequency, DF）值。本研究利用國家地震工程研究中心提供之資料針對Kg值進行計算，所得結果與中央地質調查所公布的結果略有差異，但大致上是相近的。 根據計算所得之主頻(DF)、放大倍率值(H/V)和土壤液化潛能評估Kg等資料，分別進行分類分級。相同極高級別區(DF=0.1~0.5Hz、H/V≧10、Kg＞80)，將劃分為地震極高災害潛勢級別區。同樣地，根據次等區域的條件，可以劃分為高災害潛勢級別區，接著是中災害潛勢級別區，然後是低災害潛勢級別區等。在劃分級別區的過程中，並考慮了多個參數，包括地震剪力波速（Vs30）、標準灌入試驗（SPT-N）值、灌入深度（SPT-N depth）以及地質柱狀圖中的岩層屬性（USCS 間距1.5m），以提高劃分級別區的準確性和可信度，這樣的分級結果可為都市更新優先順序和防災應用提供參考。This study utilizes Geographic Information Systems (GIS) and the Horizontal-to-Vertical Spectral Ratio (HVSR) technique to analyze historical strong earthquake data in the Taipei Basin and obtain seismic parameters (variables) such as the spectral ratio (H/V) and the dominant frequency (DF). Subsequently, using the Statistical Package for the Social Sciences (SPSS), a multivariate regression analysis is conducted to establish a model equation for the Peak Ground Acceleration (PGA) representing seismic intensity, in order to understand the impact of each variable on site-specific PGA.According to previous research by the National Center for Research on Earthquake Engineering, it is known that the distribution of the dominant frequency is mainly related to the underlying alluvial layers, and the site effects in the Taipei Basin are closely related to the Songshan Formation. In addition to alluvial layer thickness, the shear wave velocity (Vs30) of the alluvial layers also affects the magnitude of the dominant frequency. Under the same alluvial layer thickness, gravel deposits have higher dominant frequencies compared to sand and gravel deposits. Therefore, when selecting the dominant frequency, Vs30 must be considered as one of the reference values.Furthermore, soil liquefaction sensitivity is also one of the factors contributing to seismic hazard potential. According to Nakamura's research (1996), the soil liquefaction potential evaluation value Kg can be calculated using the formula Kg=Ag²/Fg, where Ag represents the amplification factor of the dominant frequency (H/V ratio), and Fg denotes the dominant frequency (DF). In this study, the provided data from the National Center for Research on Earthquake Engineering are used to calculate the Kg values, and the results obtained show slight differences compared to the results published by the Central Geological Survey, but the overall research findings are similar.Based on the calculated fundamental frequency (DF), amplification factor (H/V), and soil liquefaction potential assessment (Kg) data, classification and grading were conducted. Areas with the same extremely high levels (DF=0.1~0.5Hz, H/V≧10, Kg＞80) were categorized as zones with extreme seismic hazard potential. Similarly, based on the conditions of the secondary regions, they were classified as zones with high seismic hazard potential, followed by zones with moderate seismic hazard potential, and then zones with low seismic hazard potential. In the process of zoning, multiple parameters were considered, including seismic shear wave velocity (Vs30), standard penetration test (SPT-N) values, penetration depth (SPT-N depth), and rock layer properties in the geological column chart (USCS spacing 1.5m), aiming to enhance the accuracy and credibility of the zoning classification. Such classification results can provide references for urban renewal priorities and disaster prevention applications.