預測地震之發生對防災科技而言相當關鍵。根據多年來之研究，位於板塊邊界花東縱谷之池上斷層有機會成為探討斷層潛移與地震活動關聯性研究之最適場所。為瞭解地下流體與潛變間之關聯性，九十六年度已開始於錦園地區進行了一系列調查、監測以及人為擾動(抽注水)之水力-力學偶合試驗。根據地形分析、地表調查、電阻探測、鑽孔岩心、地表(creepmeter)與地下位移(TDR)觀測以及上下盤與斷層帶中孔隙壓力變化觀測結果，池上斷層錦園監測站可以區分出數個水力單元，水力特性具有高度的異質性，這些水力特性異質性與錦園地區之沖積物堆積、侵蝕與變形過程有關。另一方面，斷層帶附近之水力傳導特性具有隨時間變化而變化之趨勢。斷層帶所監測到的孔隙水壓變化，明顯較上、下盤為劇烈，推測此一異常現象可能與材料受壓產生超額孔隙水壓有關。同時，監測期間發現了兩次潛變事件，孔隙壓力於潛變事件前快速增加，而潛變事件一開始，孔隙水壓即快速下降，此一結果似乎暗示斷層帶受剪膨脹可能扮演重要角色。另一種可能性是扮隨斷層活動所產生之地層滲透性增加，造成超額孔隙水壓快速消散。本計畫將進行重覆性微水試驗，以進一步瞭解斷層潛變對水力特性之影響。同時，本研究增設水壓計、地表位移計以及雨量計，以長期自動監測水力-力學偶合效應分析所需之資訊，另外，本研究將裝設四組高精度地表傾斜計，以精確掌握微小的地表變形訊號。最後，利用彈性孔隙介質理論，綜合解釋觀測物理量之變化，以瞭解孔隙水壓以及有效應力對斷層潛變行為影響所扮演之角色，以成功模擬池上斷層潛變行為。預期本研究成果對於池上斷層潛變行為之瞭解將產生重要貢獻。 ; Increasing the abilities for predicting earthquake is important for earthquake hazard mitigation. The long-term monitoring in Chihshang active fault provides a good opportunity to look inside the relationships between surface creeping behaviors and earthquakes. Some interesting phenomena do reveal the mystery between surface creep of the Chihshang active fault and earthquakes. To better understand the role of fluids in the creeping of Chihchang fault, subsurface geophysical investigation, in-situ hydraulic tests and long-term pore water pressure, and deformation monitoring were conducted in 2007. Five boreholes were drilled at a depth of 30-100 m through the Chihshang fault zone at the Chinyuan site. Pore pressure variation in the shear zone, hangingwall and footwall of Chihshang fault were monitored in hydraulic observation wells and Casagrande type piezometers, accompanied with surface electrical tomography. Creeping was monitored with both creepmeters at surface and time-domain-reflectometry (TDR) cables grouted in boreholes. Based on the integrated geological and hydrogeological site characterization, the sedimentary units were characterized into several hydraulic domains. The characteristics of these hydraulic domains are dominated by the origin of stratification, erosion and deformation induced by the active Chihshang fault. These hydraulic domains show a high variability of hydraulic properties. Beside, the hydraulic properties were changed with time. In the fault zone, high total head and high fluctuation of the pore pressure were observed. We speculate that the compression-induced contraction in the shear zone is responsible for the abnormal high pore pressure distributed in the fault zone. Besides, two creep events were observed following heavy rainfall. However, the pore pressure dropped immediately when the creep events begin. This indicates that the shear-induced-dilation during creep events might play a certain role on this aspect by generating the negative excess pore pressure or opening the “valve”and releasing the overpressure within the fault zone. This research proposed a long-term monitoring plan for exploring the hydro-mechanical behavior of Chihshang active fault in Chinyuan site. The influence of the creeping fault on the hydraulic properties of sediments can be evaluated by repeated slug tests. Automatically record the required information for the poroelastic analysis induced by rainfall by rain gage, pressure transducers, and displacement transducers are proposed. Four high resolution tiltmeters are plan to install in Chinyuan site to measure the small variation of the surface deformation. Integrated interpretation will be utilized to explore the role of pore pressure, as well as the role of effective stress, on the creep events of the Chihshang fault observed in Chinyuan. It is anticipated that the results from the proposed study will largely enhance the ability for interpreting the creep phenomenon of an active fault. ; 研究期間 9708 ~ 9807
