論文提要內容： 本研究使用微地動量測之方法，針對埔里盆地所作之場址放大效應趨勢之研究和探討，以獲得更多相關的資料，希望藉此能對地震時埔里盆地的場址效應有更深入之了解，並可作為將來埔里地區建築物耐震設計與未來土地使用規畫之參考。 本研究總共在埔里盆地內選取215個觀測站（大範圍盆地內112個，小範圍埔里市區103個），使用單站頻譜比法分析得到各測站之平均頻譜比，再依不同需求選定幾個特定之頻率，將不同測站同一頻率之振幅比值挑出，並做成等值圖，藉以得知埔里盆地在不同頻率下震波放大之趨勢，主要將結果分成兩部分探討。 第一部份是以大範圍之整個盆地為主，將整個埔里盆地分成S1、S2、S3和S4四區對盆地之區域場址效應做探討，將結果與前人文獻做比較，並對結果做資料偏差之討論。分析結果可得，在盆地內長週期之放大高區多在河流沿岸和河流匯流處附近，尤其在南港溪與眉溪附近長週期之場址放大效應更為明顯。可能為埔里盆地之地形向西傾，所有河流最後皆匯流成南港溪從盆地西側流出埔里盆地，導致河道附近常期河水沖積，沖積層較為軟弱，地層速度較低之原故。 第二部份是以小範圍的埔里鎮市區為主，將市區內各測站所得之頻譜比等值圖與921集集大地震埔里市區房屋損壞情形之資料做比較，且對結果做資料偏差之討論。綜合上述之結果，去除結構物本身之問題例如：結構物年齡、形狀、結構設計、施工品質…等，結果顯示埔里市區內建築物損壞和地區場址效應有著密切之關聯。 Using microtremor measurement to study the site effect in Pu-Li basin We used microtremor measurement to study the site effect in Pu-Li basin, so as to obtain more information and to understand the local site effect during earthquake in Pu-Li basin. Furthermore, the analyses of site effect can be taken as reference for the seismic resistance design and reducing damage from earthquake. In this study, we set 215 stations (a wide range in whole basin has 112 stations ; a narrow rang in Pu-Li downtown has 103 stations). The microtremor data were analzzed by horizontal to vertical (H/V) spectral ratio of. Then, choosing several specific frequencies draw the H/V spectral ratio contour. We divided the result into two part to discuss to understand the tend of seismic waves amplification in difference frequency in Pu-Li basin. The first part for whole basin, we divided Pu-Li basin into 4 areas (S1, S2, S3 and, S4) to discuss the local site effect including the standard deviation of result. The result show that most of long period amplifications are along the rivers or near the rivers junction. The reason is due to the alluvium in these areas are thicker or the velocity are smaller. The second part is downtown. We compared H/V contours with the situation of buildings damage in Pu-Li during the Chi-Chi earthquake. The results show that there are close relationship between the buildings damage and local site effect in Pu-Li downtown area.
