- 學位論文
恆春地震引致赤山觀測井地下水位變化之數值模擬
Numerical Analysis on Groundwater Table Variations in Chih-Shan Observation Well, Induced by the Hengchun Earthquake.
摘要
台灣地區地狹人稠，山脈多而平地少，且位處於歐亞大陸板塊與菲律賓海板塊交界處。菲律賓海板塊在台灣東北方沿琉球海溝隱沒至歐亞大陸板塊下；在南方則沿馬尼拉海溝仰衝於歐亞板塊上。在此兩處隱沒帶作用影響下，使得台灣島周的造山運動相當興盛，尤其斷層錯動引起之地震相當頻繁。地下水位在地震前後產生異常變化的例子很多，此一現象一般被認為是由於地殼累積之能量在地震時釋放，改變大地應力分布，產生應變而引起孔隙水壓的激發，進而造成地下水位的變化。 賴岳廷(2007)利用 FLAC 數值軟體建構之Finn模式孔隙水壓力動態反應模式的概念模型進行動態分析，其成果與實際地下水位變化量彼此符合程度佳，但僅能描述水位階變情形。陳德偉(2008)根據Biot理論建立斷層錯動模式之數值分析方法，對於地層剪應變、塑性區等現象有合理的模擬成果，對於水位變化量符合程度不佳，對水位震盪的情形能有適當的模擬。本研究建基於前述成果，根據新設屏東平原地下水觀測井赤山站於2006年恆春地震事件觀測所得之秒水位資料，收集各項性質參數，未有資料者則予以合理假設，測試在使用Finn模式與Biot模式兩種不同理論下，測試概念模型對於水位細部變化之適用性，期望在地震引起地下水位變化之數值模擬上，能有更進一步之認識。 由本研究數值模擬成果，Finn模式之水位變化量普遍大於由監測記錄算出之結果，Biot模式水位變化量則多較監測記錄來的低。Finn模式出現較顯著的階變現象，但對於水位的震盪情形，Biot模式有較佳的模擬表現。針對柏森比進行參數分析，在土層柏森比越大時，水位變化量大致呈現出上升的趨勢。若與地表地震紀錄彼此對照，Finn模式對於動態作用力反應較為即時，Biot模式則會延遲。整體而言，本研究所選擇參數對於赤山觀測井之模擬不佳，仍須進一步參數研討，方能得到較精確之模擬成效。
並列摘要
Since located at the borderline between Eurasian Plate and Philippine Sea Plate, the orogeny is very active in the area and earthquakes caused by dislocation of geologic faults frequently occurred. The groundwater-level variation is one of the characteristics induced by earthquakes. The cause of this phenomenon is generally considered as the energy stored in the crust would be discharged when earthquake occurred, which altered the earth stress distribution, thus, the developed excess pore pressure led to groundwater-level change. Lai(2007) conducted a dynamic analysis using FLAC program to develop a numerical model of excess pore pressure based on Finn theory, the results confirmed the model provided a fine simulation of the hour-recorded groundwater-level change in Jhuo-Shuei River alluvial fan caused by Chi-Chi earthquake, but no good description for oscillation. Chen(2008) developed a fault thrusting model and applied Biot theory, his model had rational simulation for the pore pressure fluctuation, but the amount of pore pressure changes was different. For understanding of groundwater-level changes caused by earthquakes, this research conducted numerical analysis based on two different theories of pore pressure generation, and compared the simulation results with the data from the high-frequently monitoring Chih-Shan observation well for the groundwater-level change caused by Hengchun earthquake in 2006, Dec. 26. The Finn mode simulation results were generally larger than the water-level change recorded, contrarily the Biot mode had a lower water-level change simulation compared to the record. The oscillation phenomenon of groundwater was better described by the Biot mode, while Finn mode provided better description for stepwise groundwater change. Parametric study for poisson’s ratio suggested little influence. The Finn simulation had better corresponding result with the earthquake record than those of Biot simulation. In conclusion, the parameter used in this research were not able to provide good results, it would be necessary to further consider proper soil parameters improving simulation.