本研究主要是參考美、日兩國之經驗，以地震儀陣列量測微地動資料來推估淺層沈積層之剪力波速度構造之方法。包括從野外施測步驟，反覆驗證後取得測區之微地動資料，到室內進行頻率-波速分析求取表面波頻散曲線，然後執行多次基因演算法逆推得淺層剪力波速度構造，最後以傳統表面波頻散曲線逆推技術，進一步修正此速度模型。 本研究主要施測的地區為台北關渡(關渡大橋北岸右側數百公尺空地上)及921受創嚴重的埔里盆地，在研究中發現近地表之剪力波速度應呈梯度增加之形態；以關渡地區為例，在深度約400-700公尺處應為基盤之所在位置，而埔里盆地地區，則在不同深度(10-25公尺)會碰到約1.0-1.4km/s之高速層(礫石層)。但詳細深度必須有更低頻之訊號才能解析得出。目前結果只能確定該處應有-『高速基盤』，如此計算的頻散曲線才能與陣列觀測的相速度吻合。 Follow Japan and United States seismologists` experience, We developed a method to estimate the near surface sediment`s shear wave velocity structure by using microtremor data which measured from a portable seismic array. This method includes the data acquisition procedures for the field works and the analysis in the laboratory. The analysis procedures can be categorized as (1) Frequency-Wavenumber analysis to get the dispersion curve, (2) to search the good velocity models using genetic algorithm, and (3) to refine the GA searched model using traditional surface wave inversion technique. In this study, we applied our method to Guendu, Taipei and Puli basin. Puli basin is seriously damaged the 921 chi-chi earthquake. From our analysis, we found that the velocity is gradually increasing for the near surface sediments. The results show that the high speed basement appear in the depth of 400-700m for Guendu, and roughly about 10-25m deep for Puli basin.
