利用微地動量測探討台北盆地之場址效應

Using Microtremor Measurement To Study The Site Effect In TheTaipei Basin

林士棋(Shih-Chi Lin)

指導教授 ： 溫國樑

國立中央大學/地球科學學院/地球物理研究所/碩士(2006年)

摘要

本研究台北盆地，藉由單站頻譜比法分析微地動資料，來探討台北盆地場址特性，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，單站頻譜比法是方便又省時之方法，尤其當研究區域位於沖積層上，不易尋得雙站頻譜比法所須之岩盤參考測站時，提供了快又有效的研究方式，而且又對於地震少之地區在場址研究上有很大的幫助。
由台北盆地微地動測量結果得知，主頻分佈主要與底下沖積層有關，而台北盆地之場址效應與松山層有很密切的關係。主頻分佈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。盆地邊緣地勢較高的地區、或山區，底下沖積層淺薄，因此主頻較高。盆地西北部(關渡、蘆洲、五股工業區、新莊)、盆地東邊的松山區、板橋地區主頻較低，約介於0.4～0.8 Hz，顯示此地區沖積層較厚或地層較軟、速度較低。信義計畫區主頻約0.8Hz～2.0Hz。盆地北部、東北、南部靠近盆地邊緣地區為主頻較高地區，約介於2.0～6.0 Hz，顯示此區沖積層較薄或地層較堅硬、速度較高。
液化潛能敏感極高地區由西到東為士林區士林夜市附近、內湖區與中山區和松山區交會處位置約在內湖高工、內湖地區的中央約在成功路四段地區。需注意建築物的安全規劃。

關鍵字

場址效應 ； 微地動 ； 土壤液化 ； 頻譜比

並列摘要

We used microtremor measurement to investigate the site effect in Taipei basin 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 589 points respectively, and analyzed the site effects. The dominant frequency of site effect in the Taipei basin is very close relation to the sungshan formation.
The distribution of the dominant frequencies shows that the areas near the basin edge have a higher dominant frequency. It is about 2.0~6.0Hz near the basin edge in the north, east and south. The western part of the Taipei basin, Sungshan area and Banciao area show a low dominant frequency in the contour map, it is about 0.8~2.0Hz.
We also calculated the “Kg value” (Nakamura, 1996) for estimating the earthquake damage of ground liquefaction area. In this study, Kg value is greater than 80, it had good correlation to compare with drilling.

並列關鍵字

microtremor ； H/V Ratio ； liquefaction ； site effect

參考文獻

Chen, W.F. and Louis L. Teng (1990) Depositional environment of Quaternary deposits of the Linkou Tableland, northwestern Taiwan: Proc. Geol. Soc. China, vol33, no.1, 39~63.

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Lermo, J. and F. J. Chavez-Garcia, (1994). Are microtremors useful in site response evaluation, Bull. Seism. Soc. Am., 84, 1350-1364.

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