集集地震地下水位變化與地表變形之關聯

Groundwater-Deformation Coupling in the Seismogenic Processes of the 1999 Chi-Chi Earthquake, Taiwan

陳界宏(Chieh-Hung Chen) ； 汪中和(Chung-Ho Wang) ； 溫世忠(Strong Wen) ； 葉大綱(Ta-Kang Yeh)

《工程環境會刊》 34期 (2015/01) Pp. 27-34

https://doi.org/10.6562/JEE.2015.34.2

摘要

當地層受應力擠壓，超過斷層可以負荷的限度，就會形成地震。地下水位及地表變形都對應力非常敏感，是反應地震相關應力累積過程的良好指標，本研究利用台灣35個地下水井的水位資料，以及15個全球定位系統（GPS）觀測站的數據，探討在1999年集集地震（Mw7.6）發生前，地下水位及地表變形的對應關係。利用數據分析工具，先將與應力無關的信號濾除。剩餘與應力有關的訊號，可以清楚觀察出有29口觀測井的地下水位及GPS地表變形紀錄，在集集地震前一年內，在時間域及大尺度範圍上有非常好的對應關係。當地殼受到擠壓（或拉張）時，地下水位會隨之有上升（或下降）的現象。從集集地震的孕震過程來觀察，自震前350日開始，先有輕微的擠壓作用，隨之發生強烈的拉張，接著產生強烈的擠壓，直到超過車籠埔斷層的承受極限，地震發生。因此，集集地震的事件提供了一個極佳地下水位與地表變形的震前耦合案例，可做為探討未來大地震前兆的重要參考。

關鍵字

地震前兆 ； 地表變形 ； 地下水位變動 ； 震前耦合 ； 集集地震

並列摘要

Earthquakes usually occur abruptly when cumulative stress loading on strata exceeds what faults are able to withstand. Because groundwater levels and surface deformation are sensitive to changes in stress, 35 groundwater wells and a global positioning system (GPS) consisting of 15 stations are utilized to examine the seismogenic process of the 1999 Chi-Chi earthquake (Mw 7.6) in Taiwan. Responses of signals that are unassociated with stress changes are removed from the groundwater and deformation data. The derived stress-related residuals show that pre-earthquake phenomena with consistent variations in the time domain can be simultaneously observed across large spatial scales. Signals appeared in groundwater levels at 29 wells and in the orientations of surface deformation at GPS stations starting approximately 350 days prior the Chi-Chi earthquake. Compression (or tension), determined by the orientations of surface deformation accompanying rise (or lowering) of water levels, suggests that the groundwater-deformation coupling is strong, and pre-earthquake phenomena can be detected. The seismogenic process of the Chi-Chi earthquake is characterized by stress in a sequence of slight compression, intense tension, severe compression and rapid approach to the Chelungpu fault threshold. Thus, Chi-Chi earthquake is a unique case to comprehend the complete seismogenic process in the pre-earthquake coupling between groundwater-deformation, and can serve as an important reference for future disastrous earthquakes in Taiwan.

並列關鍵字

Earthquake Precursory ； Surface Deformation ； Groundwater Variation ； Pre-Earthquake Coupling ； Chi-Chi Earthquake