| 摘要: | 本計畫針對92年度計畫中地震-地下水關係研究所得心得與更新觀點進行更深入研究，以瞭解地震-地下水之關係及發生機制，提升同震水位量測、分析之技術。共有三項主要研究:(1)研發破碎含水層之地震水井水力學模式及理論。目前的地震水井水力學模式主要研究地震表面波通過未固結、顆粒性含水層所造成的地下水壓力變化。許多地震觀測相關用井多與多孔隙岩體母質及散佈期間之破裂帶、節理組成之破碎含水層相通；如曾文水庫應變儀所在位置的含水層即是一例。破碎含水層水井水力學模式及相關之地下水理論與顆粒性含水層者大不相同，因此實在需要有適當的破碎含水層地震水井水力學理論以瞭解相關之同震水位變化及資料分析之用。擬使用雙孔隙率模擬方法發展破碎含水層之地震水井水力學模式，決定其解析解及同震水位分析方法。(2)井中不同深度之同震水位分析與修正。目前已知的諸多同震水位相關研究僅使用單一壓力計量測同震水位，忽略井中水壓隨深度變化現象。中央大學地下水研究井場同震水位觀測井之不同深度壓力計量測得知不同深度有不同水壓變化。顯示高頻、快速震盪水壓變化屬動態壓力，而壓力計輸出的水位屬靜態壓力轉換，故須經過修正方能代表井中真正的同震水位。本計畫將分析壓力計之靜態水位資料對同震水位分析的誤差，建立動態壓力與真正水位的關係，並發展修正方法以正確調查、瞭解相關問題。(3)地震-地下水位變化機制探討：大地震發生時地下水位的變化或與地震源的斷層錯位形成的體應變有關，或與地震波通過後造成孔隙壓的變化有關，尚未有定論。在探討地下水位觀測與地震前兆研究前提下，地震—地下水位變化機制實為重要的基本議題。我們擬針對規模大於六的台灣地震進行一系列的震源、斷層錯動引發的體積應變及各地的加速度及速度值分佈進行分析，以瞭解其所屬區域之地下水位可能的變化並決定可能之發生機制。 From the results and renewed concepts obtained in the last-year project, it is understood that analysis and measurement of co-seismic water levels require more advanced theory and techniques, and the possible mechanisms causing earthquake-groundwater level variation need to be established. The current project concerns with three major research topics: (1) Development of a new seismic well hydraulics theory in fractured aquifers. The currently available seismic well hydraulics theories are limited to the unconsolidated, granular aquifers. But many wells for seismic studies are installed in the fractured zones in porous rock. For example, the bore hole hosting the strain meter at the Tsang-Wen Reservoir is in such a fractured aquifer. Thus it is important to establish seismic well hydraulics theories in fractured aquifers, which will be significantly different from those in granular aquifers. We will use the double-porosity approach to develop a seismic well hydraulics model for fractured aquifers, and determine its solutions and the method of analyzing the co-seismic water level data. (2) Analysis and correction of water level data at different depths of a well. It is noted, in the currently available studies, that co-seismic water level was measured using only one water pressure transducer in a well, thereby ignoring the possible variation with depth. At the Groundwater Research Well Field in the National Central University, we installed three transducers at three different depths in one well, and they yielded different co-seismic water levels during earthquakes. This reveals that the high-frequency, rapidly-oscillated water pressure is probably dynamic water pressure. However, output of a water pressure transducer is based on the hydrostatic pressure conversion. To correct this problem, we will collect more depth-dependent co-seismic water level data, analyze them, and then develop a method to compensate the water pressure transducer output for true co-seismic water level measurement. (3) Investigation the possible mechanisms causing the earthquake-groundwater level variation. It is not clear how the earthquake can influence groundwater level variation- whether it is caused by the fault dislocation at the epic center or by the pore water pressure change due to the earthquake wave is under debate. The mechanism causing the earthquake-groundwater level variation is imperative for precursor study. We will analyze the volumetric strain, displacement, and acceleration of earthquakes with a magnitude greater than 6 in Taiwan, and find explanations for the possible mechanisms. 研究期間：9302 ~ 9312 |
