超低頻電磁波遙測技術應用於地層下陷潛勢區之研究-以濁水溪沖積扇為例

彰化雲林地區地層下陷問題長年為民眾及政府所關切，經濟部水利署地層下陷防治工作自1995年開始，近年地層下陷問題已有明顯減少。目前的地層下陷監測方法包括精密水準測量、雙頻GPS固定追蹤站、雷達干涉測量、磁環分層式地層下陷監測井和深層水準樁各有其限制，需相互搭配使用才能得知地表變遷以及地下的情況，且無法得知監測井深度300m以下之地層壓縮資訊。超低頻電磁波遙測技術探勘方法具有非破壞性，速度快、範圍廣、可探測地下深度較深和不受結構與地形影響之優點，適合用於地層下陷區的探測。本研究採用區域性探勘及設置監測站兩種模式，區域性探勘範圍北至彰化埔鹽，南至雲林水林，選定相關因子後分別進行多元線性迴歸和地理加權迴歸，將地應力變化與現有下陷資料進行比對；超低頻電磁波監測站於彰化溪州與雲林土庫設站搜集資料，進行長時間監測，將地應力變化與現有地層下陷資料進行比對。所得成果發現於區域性探勘時，土壤液化潛勢、地下水變化、大型交通建設路過與否和下陷變量皆為影響地應力變化的相關因子，將地應力變化與下陷變量資料進行比對，兩者呈現正相關；超低頻電磁波監測站則發現地應力變化與GPS下陷變量呈現正相關。超低頻電磁波遙測方法可透過測得之地應力變化快速推估出地層下陷變化，此法可使用於區域探勘、不同深度的探勘以及高時間抽樣的探勘，靈活性高，為一新型遙測技術。

關鍵字

地應力；電阻率；地下水；地質災害；天然電磁場

並列摘要

The problem of land subsidence in the Changhua and Yunlin area has been concerned by the people and the government for many years. The prevention of land subsidence by Water Resources Agency, Ministry of Economic Affairs has decreased significantly since 1995. The current land subsidence monitoring methods include precision leveling, dual-frequency GPS stations, radar interferometry, the continuous land subsidence magnetic ring station and the land subsidence deep benchmark. Each has its own limitations. They need to be used in conjunction with each other to know the surface changes and underground conditions, and it is hard to know the formation compression information of the monitoring well below 300m. The ultra-low frequency electromagnetic wave remote sensing technology survey method has the advantages of non-destructive, fast speed, wide range, can detect deep underground depth and is not affected by structure and topography, and is suitable for the detection of land subsidence areas. This study adopts two modes of regional exploration and setting up monitoring stations. The scope of regional exploration includes Changhua and Yunlin. After selecting relevant factors, multiple linear regression and geographically weighted regression are used, and compare the change of crustal stress with the existing subsidence data. The ultra-low frequency electromagnetic wave monitoring stations are set up in Changhua Xizhou and Yunlin Tuku to collect data, conduct long-term monitoring, and compare the change of crustal stress with existing land subsidence data. In the regional exploration, the soil liquefaction potential, groundwater changes, large-scale traffic construction passing or not, and subsidence changes are all related factors affecting the changes of crustal stress. The data on crustal stress changes and subsidence changes are compared. There is a positive correlation; the ultra-low frequency electromagnetic wave monitoring station found that the crustal stress changes arepositively correlated with GPS subsidence changes. The ultra-low frequency electromagnetic wave remote sensing method can quickly estimate the change of land subsidence through the measured crustal stress changes. This method can be used for regional exploration, exploration at different depths, and exploration with high time sampling. It has high flexibility and is a new type of remote sensing technology.