利用微地動量測探討台灣中部地區之場址效應; Using Microtremor Measurement To Study The Site Effect In The Central Taiwan

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题名:	利用微地動量測探討台灣中部地區之場址效應;Using Microtremor Measurement To Study The Site Effect In The Central Taiwan
作者:	涂嘉勝;Chia-Shung Tu
贡献者:	地球物理研究所
关键词:	頻譜比;土壤液化;微地動;場址效應;microtremor;spectral ratio;site effect;liquefaction
日期:	2005-06-23
上传时间:	2009-09-22 09:55:12 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	1999年集集地震對台灣中部地區造成相當大的災害，包含了建築物損害、人員傷亡以及經濟財產的損失等。地震過後我們可發現在車籠埔斷層下盤地區之地動加速度比起上盤地區明顯小很多，但是在下盤地區仍有許多的建築物損害。因此我們為了暸解此區地震後造成相當大的災情是否與局部之場址效應有關，本研究乃於台灣中部地區分布500個微地動測點，且利用單站頻譜比法分析微地動資料，希望能夠藉此瞭解研究區域內之場址特性，並與集集地震災害分布來做比較。由微地動量測所獲得之主頻分布圖，可以得知在台中盆地北部、后里台地西部、大肚台地以及八卦山台地北部主頻約8?16 Hz；西部麓帶約3.5?7 Hz；台中盆地南部約2?5 Hz；清水及彰化海岸平原約0.5?2.5 Hz。同時本研究也計算出值（Nakamura，1996），值可以用來評估土壤液化潛能，結果顯示當值大於20的地區與集集地震後液化地區有相當良好的相關性，因此微地動之值也提供一個可以用來評估土壤液化潛能的方法。在建築物耐震設計方面，不同高度之建築物皆有其不同的共振週期，因此本研究分別選了四個頻率（5.0、2.0、1.0、0.6 Hz）之放大倍率等值圖與不同樓高之建築物損害來做比較，結果顯示在下盤地區建築物受損主要為場址效應所引起，除了土壤液化地區之外。但在10樓以上之高層建築物受損除了與場址效應有關外，可能也與應力傳遞及人為施工不良有關，是否真為如此以後仍需更近一步研究。希望本研究結果可作為將來地震防災、建築物耐震設計、土地使用規劃以及土壤液化潛能評估之參考。 Central Taiwan suffered very severely damages during the Chi-Chi earthquake in 1999. It includes buildings collapsed, casualties, and economic loss, etc, and the Chelungpu fault ruptured during this earthquake. Although the ground motions in the footwall area were smaller than that in the hanging wall area. But the Taichung area which located in the footwall also has many building damages occurred. In order to obtain more information and understand the local site effect during earthquake, we performed the dense microtremor measurement in the Central Taiwan area. In this study, we set about 500 microtremor stations. By using the horizontal to vertical spectral ratio（H/V Ratio）, we can analysis the site response in the central Taiwan. The site response can be used to compare with the ground motion response and the damage distributions of the Chi-Chi earthquake. The dominant frequency and amplification factor at each station were calculated. From the dominant frequency contour map shows that at the north of Taichung basin west of Houli tableland, Tatu tableland, and north of Pakuashan tableland, the dominant frequency are about 8 ~ 16 Hz; the western foothill zone is about 3.5 ~ 7 Hz; the south of Taichung basin is about 2 ~ 5 Hz; Chingshui and Changhua coastal plain are about 0.5 ~ 2.5 Hz. We also calculated the “Kg value” (Nakamura, 1996) for estimating the earthquake damage of ground liquefaction area. In this study, when Kg value great than 20, it had good correlation with liquefaction area during Chi-Chi earthquake. So the Kg value of microtremor offers a good alternative for estimation of an area’s potential for liquefaction. For the purpose of the earthquake resistant design, earthquake engineers must consider the site response at a specific period. Therefore, in this study, we select 4 frequencies (5.0, 2.0, 1.0, 0.6 Hz) to plot out the amplification contour map of the site response and compare with the distributions of damaging buildings during the Chi-Chi earthquake. The results show the site effect caused many building damages in foothill area during the Chi-Chi earthquake in 1999 except the liquefaction areas. Otherwise, the damage buildings’ floor higher than 10 may resulted by the stress propagation because the Chelungpu fault trace turned to right nearby the Wufong area, but we need more study in the future. On the basis of this analysis, the results can also use as a reference for the future seismic hazard mitigation, seismic safety design, land use planning, and estimate potential of soil liquefaction.
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