本研究以中央氣象局強地動觀測網的近場及遠場地震資料為依據，從Ｓ波與尾波的富利葉譜中，利用地震學頻譜比值的方法，計算宜蘭地區各強地動觀測站的場址放大效應係數，並分區探討Ｓ波與尾波場址效應係數的相關性，以及局部場址效應係數與地表地質的關係。 本研究共選取了中央氣象局強地動觀測網宜蘭地區的29個地震、25個測站的地震記錄作為研究資料，為了系統地探討蘭陽地區局部場址效應，依測站所在的地表地質及地形，將研究區域劃分成三區：Ⅰ.位於廬山層的測站、Ⅱ.蘭陽平原中心至平原邊緣連線上的測站群、以及Ⅲ.南澳附近的沖積層測站，並討論各區的局部場址效應。各記錄分別取出Ｓ波與尾波的頻譜值後，依據地表地質的條件，選取位於廬山層地層上的測站ILA052作為參考站，將其他各測站的Ｓ波與尾波頻譜值與參考站的頻譜值相比對，得到Ｓ波及尾波的場址效應係數。分析並討論這些頻譜比值資料之後，得到下面結論： 1.Ｓ波頻譜比與尾波頻譜比在各頻率段均可看到相同的起伏變化情形。 2.位在平原中心的測站有低頻場址放大的現象，此低頻放大現象應與盆地構造有關。 3.測站的場址效應除了與地表地質有一定的相關性之外，還會受到其他因素（如地表地形、沖積層覆蓋、不同地層的震波傳遞速度以及地下構造形貌等）的影響，所以場址效應的相關因素應該說是多重而複雜的。 4.Ｓ波與尾波頻譜比的計算結果，得到相當一致的場址效應係數。 5.強地動觀測資料的尾波部份進行分析研究，其優點在於各測站之加速度記錄均有絕對的地動值，不需要作繁雜的儀器放大倍率的修正，對於尾波振幅資料的研究方面甚為方便。 This study used the near and far field data recorded by the Taiwan Strong Motion Instruments Program (TSMIP) of CWB (Central Weather Bureau). We used the Spectrum Ratio to calculate each site amplification coefficient between a reference rock site and each soil site of the Lan-Yang Plain from Fourier spectrum of S waves and Coda waves. The relationship between the site effect factor of S and Coda waves and surface geology in different areas was analyzed in this study. The data used were recorded by the TSMIP accelerographs of CWB from 29 earthquakes and at 25 stations on the Lan-Yang Plain. According to the surface geology, the sites of Lan-Yang Plain was divided into 3 areas:Ⅰ. sites on Lushan Formarion; Ⅱ. sites from the basin center to basin edge; Ⅲ. sites near by Nanao alluvium. Based on surface geology, I chose ILA052 to be the reference site. The results from the spectrum ratio of each soil site and the reference site in this study are summarize below: 1.The S wave and Coda wave Spectral Ratios are similar on different frequency bands. 2.There is site amplification in low frequencies on the central part of the plain. This site effect is probably related to basin structure. 3.The site effect was not only related to surface geology but also other causes (e.g. surface topography). The causes of site amplification effect are many and complex. 4.There are the same site amplification factors which were obtained by the spectral ratios of S waves and Coda waves. 5.The advantage of using Coda waves of strong motion records to analyze site effect is that each acceleration record at different sites has absolute ground motion value. It is not necessary to correct the instruments response. It is convenient to study the Coda wave amplitudes.
