本研究區域為桃竹苗地區，想藉由Nakamura（1989）所提出單站頻譜比法分析微地動資料，來探討當地場址特性，結果可提供將來建築物耐震設計以及土地使用規劃之參考，並配合Nakamura（1996）提出的Kg值計算方法，就能夠快速簡便的分析場址的液化潛能指數。在研究場址放大效應上，單站頻譜比法是一省時又省力之方法，尤其當研究區域位於沖積層上，不易覓得雙站頻譜比法所須之理想岩盤參考測站時，其提供了一快又有效的研究方式，而且其又可利用微地動資料進行場址之研究，對於地震少之地區在場址研究上有很大的幫助。 桃竹苗地區微地動測量發現，主頻分布主要與底下沖積層有關，地勢較高的山區、臺地或丘陵，底下沖積層淺薄，因此主頻較高，例如林口臺地、飛鳳山丘陵等；溪流附近或濱海沖積平原，沖積層厚，主頻則較低，例如頭前溪流域、後龍溪流域等。另外，主頻分布圖顯示在桃園地區西半部主頻介於7.0~15.0 Hz之間，反應淺部地表層的放大效應；東半部主頻則約介於1.0~2.5 Hz之間，反應底下深層的放大效應。主頻分布除了與沖積層厚度有關之外，沖積層剪力波波速也是會影響主頻大小，相同的沖積層厚度，礫岩堆積會比砂泥堆積主頻來的大。 Kg值指出各縣市具高度危害度地區。桃園縣雖然沒有明顯的Kg值高區，但仍需多加注意濱海區域；新竹縣市Kg值高區分布在新竹市北區、新豐鄉及新埔鎮與芎林鄉交界；苗栗縣液化潛能危害地區則位於竹南鎮南部、後龍鎮北部、苗栗市部分地區到西湖鎮一帶。 We used microtremor measurement to investigate the site effect in Taoyuan, HsinChu and Miaoli region by applying single spectral ratio method (Nakamura, 1989), the analyses of site effect can be taken as reference for the seismic resistance design and reducing damage from earthquake. After that, we calculated the Kg value of each site, then we can rapidly and easily obtained the local liquefaction vulnerability index. In this study, we performed measurement on 418 points respectively, and analyzed the site effects. The contour of dominate frequency is related to the topography. The alluvial plan areas exhibited low dominate frequency for its thick alluvium, and the tableland areas showed high dominate frequency for its thick alluvium contrarily. Besides influence of the thickness, the velocity of S-wave also influenced the dominate frequency. The dominate frequency of conglomerate is larger than sandstone with the same thickness, for example. Kg values have been proposed by Nakamura(1996) and are simply derived from strains for accurately estimating earthquake damage of surface, and be considering to the vulnerability index of site. In this study, we investigated the vulnerability index by applying to Kg method.
