國內外許多地震事件中，經常發現地下水位在地震發生前後，有異常變化之現象。1999年集集地震發生時，由經濟部水資源局在鄰近於車籠埔斷層西側的濁水溪沖積扇建立之地下水位監測井網，恰好紀錄了濁水溪扇洲於地震期間之水位變化。
　　為了解地下水位變化與地震之關係，本研究利用有限元素分析軟體PDEase2D建構出動態孔隙彈性理論模式，針對地震引發地下水位變化進行物理機制分析。主要分析分為三部分，第一部分為敏感度分析，藉由應力-應變-超額孔隙水壓變化之耦合關係，探討各參數對同震地下水位變化之影響；第二部分是假設不同邊界條件，以探討地層環境對同震地下水位變化之影響；第三部分為複層地層分析，探討不同的沉積模式對同震地下水位變化之影響。此外，本研究以濁水溪沖積扇做為研究案例，針對集集地震所引發的地下水位變化進行水位擬合，以求得各觀測站區域之修正值。
　　分析結果顯示，水力傳導係數、楊氏係數、體積應變放大係數、阻尼係數及作用力大小，對同震地下水位變化的影響較為顯著。此外，施加不同型式之作用力會產生不同之震波型式，進而影響地下水位變化的趨勢。對均質地層而言，越靠近力源處其同震地下水位變化越劇烈，且透水性越差，其同震地下水位變化越明顯。對於非均質地層而言，不同性質之地質材料於地層中所佔的比例、厚度與沉積組合型式，對同震地下水位變化之程度與趨勢均有明顯的影響。研究案例由於應用理論、地質模型與作用力型式均假設為較單純之情況，因此分析結果需乘以一修正值以符合現場地下水位變化之趨勢。

　　The abnormal change of groundwater level has often been accompanied with many earthquake incidents around the world. During the occurrence of 1999 Chi-Chi earthquake, a network of hydrologic monitoring wells that located in Choshui River alluvial fan near the west side of Chelungpu fault recorded the abrupt changes of groundwater level which clearly showed the effect of this major earthquake.
　　In order to understand the relation between change of groundwater and earthquake, this study attempts to develop a modified dynamic poroelastic theory. A finite element analysis software PDEase2D is employed to carry out the numerical study. The poroelastic theory features the coupled relationship of stress-strain-pore pressure change. Thus, the physical mechanism of groundwater level change due to earthquake can be interpreted satisfactorily. There are three main topics in this study. The first part is sensitivity analysis. The effects of various parameters on the coseismic changes of groundwater level are discussed. The second part discussed the effect of stratum environment on the coseismic changes of groundwater level, which assumes different types of boundary conditions. The third part is stratum analysis of composite layers. It discussed the effect of different sediment models on the coseismic changes of groundwater level. Furthermore, this study took Choshui River fan as a case study, fitting the changes of groundwater level that caused by Chi-Chi earthquake, and evaluating the regional correction coefficient of each observation station.
　　The numerical results showed that hydraulic conductivity, Young’s modulus, volumetric strain amplifying coefficient, damping coefficient and force proportion had significant effect on coseismic groundwater level. Besides, imposing different types of force lead to different types of seismic waves, and further affected the trend of changes of groundwater level. For homogeneity stratum, the changes of coseismic groundwater level would become more severe if get closer to the imposed location of applied force, and the low permeable condition also had significant effect on coseismic groundwater level. For heterogeneous stratum, the composition, thickness and sediment type of different geology materials also had significant effects on the extent and trend of the coseismic groundwater level. For the case study, since the numerical model is considered a simplistic one, therefore, this study suggests a correction coefficient be necessary for fitting in the trend of realistic changes of on-the-spot groundwater level.

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