集集地震引發河川流量異常變化

1999年9月21日01時47分在台灣中部發生芮氏規模7.3之地震，當時全台共建置了411口地下水位觀測井，其中地下水位出現同震變化的計有291口（138站），多分布於中部及西南部平原範圍由上升7.42公尺至下降11.09公尺。同震地下水位變化情況可反應出各地應力場改變或體積應變，當地層受外界壓力時，內部的應力場分布或體積應變將重新調整，同時造成超額孔隙水壓的變化，而超額孔隙水壓的消長對於河川流量的變化深具影響。檢視全台124站流量測站之日流量變化，發現34站於震後出現流量異常增加或減少之變化，分布於距離震央約5至145公里的範圍內，其中以水里橋及桶頭等2站出現震後流量異常減少之現象，其餘32站皆出現震後流量異常增加。為了解上述的現象，本研究嘗試建立簡化的概念利用有限元素近似法模擬自由含水層、部分受壓含水層及受壓含水層，分析地層側向受壓後，其有超額孔隙水壓之生成與消散，並進一步的探討超額孔隙水壓與河川流量異常之關係。本研究主要有兩個目的，第一個為震後流量異常變化之現象，另一個為造成流量異常之機制。

關鍵字

集集；河川流量異常變化；地下水；流量；地震；同震

並列摘要

An ML 7.3 earthquake occurred near the town of Chichi in central Taiwan at 01:47 September 21, 1999. Among 411 monitoring wells, 291 wells located at 138 hydrogeological stations recorded coseismic changes in groundwater level during the Chi-Chi earthquake. The coseismic changes ranged from a rise of 7.42 m to a fall of 11.09 m. Coseismic groundwater level changes may reflect the redistribution of tectonic stress and crustal strain, which may induce abnormal changes in streamflow. Changes of river discharge induced by the Chi-Chi earthquake were recorded at 34 out of 124 stream gauges in Taiwan. These 34 gauges located approximately between 5 to 145 km from the epicenter, where 32 gauges recorded surging flow and 2 gauges, Tong-Tou and Shui-Li bridge, recorded a decrease of discharge. The finite element method was adopted to analyze three different types of aquifer, including unconfined aquifer, semi-confined aquifer and confined aquifer. The purposes are to understand the process of how the lateral compression induces excess pore pressure restoration and to realize how the mechanism affect the abnormal streamflow changes. In this study, we are going to focus on two targets. One is the abnormal streamflow changes and the other is the mechanism of these changes induces by earthquakes.

並列關鍵字

Chi-Chi ； abnormal streamflow ； groundwater ； discharge ； earthquake ； coseismic

參考文獻

張天瑞 (2007) 水力發電系統介紹，物理，29(3)，689-695。

Biot, M.A., 1941, General theory of three-dimensional consolidation, J. appl. Geophys., 12, 155-164.

Bowin, C., Lu, R.S. and Lundberg, N., 1978, Plate convergence and accretion in the Taiwan-Luzon. AAPG Bull., 62, 1645-1672.

Chia, Y., Wang, Y.S., Chiu, J.J. and Liu, C.W., 2001, Changes of groundwater level due to the 1999 Chi-Chi earthquake in the Choshui River alluvial fan in Taiwan, Bull. Seismol. Soc. Am., 91(5), 1062-1068.

Hutton, David V., 2004, Fundamentals of Finite Element Analysis, McGraw-Hill Co, New York.

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集集地震引發河川流量異常變化

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