2016美濃地震引致嘉南平原與屏東平原地下水文特性變化研究;2016 Meinong earthquake induced hydrological property changes in Chianan and Pingtung plains, Taiwan

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题名:	2016美濃地震引致嘉南平原與屏東平原地下水文特性變化研究;2016 Meinong earthquake induced hydrological property changes in Chianan and Pingtung plains, Taiwan
作者:	林彥耀;Lin, Yan-Yao
贡献者:	應用地質研究所
关键词:	2016美濃地震;地下水文;PGV&PGA;水文地質特性;地潮分析;2016 Meinong Earthquake;groundwater hydrology;PGV&PGA;hydrogeological property;earth tidal analysis
日期:	2020-08-13
上传时间:	2020-09-02 19:18:03 (UTC+8)
出版者:	國立中央大學
摘要:	透過地震引致異常水文現象為了解水文地質特性的有效方法，而水文地質資料的完整性也是地震水文研究的關鍵。本研究蒐集2016高雄美濃地震震後地表與地下水文變化情形，嘗試理解地震引致台灣南部地區水文變化的機制。藉由分析第一含水層之同震水位變化之空間分布，以及地表破裂與液化噴砂之位置，可以發現同震水位變化主要發生在震央西北部的嘉南平原，而許多的液化與破裂點位位於新化斷層沿線。將液化點位與尖峰地動加速度與尖峰地動速度(PGA,PGV)的內插結果進行比較，結果顯示液化事件與PGV之關聯性較高。細究其數值則顯示引發液化事件之PGA門檻值約為150 cm/s^2，而PGV之門檻值約為40 cm/s。另外，新化斷層周圍數個地下水井中，部分深部含水層井位觀測到的水位變化不同於其他嘉南平原之水井呈現整體水位上升的情形，反而顯示同震水位下降，其位於淺部含水層的井位則顯示同震水位上升。其中，新化與那菝兩井顯示出不同深度的地下水位於震後變得靠近的現象，可能為不同含水層在震後變得連通而產生垂向的水壓傳遞所致。而我們對於含水層間連通性變化的推測，可以藉由以地潮分析不同含水層地下水位得出的相位差結果驗證，並且估算震前與震後含水層之導水係數變化情形，以此探討地震對於區域含水層的影響。結果顯示，新化井不同深度含水層之相位差變化趨勢於震後變得相似，代表新化井不同深度之含水層於地震後因裂隙而產生垂向連通，並引起地下水位變得相近。;The observations of hydrological anomalies induced by earthquakes are valuable data to investigate the hydrogeological properties. In this research, we collected the hydrological data before and after the Mw 6.4 2016 Meinong Earthquake. The main purpose is to investigate the mechanism of hydrological changes triggered by earthquakes. From the distribution of groundwater level changes at the first aquifer, as well as the distributions of the surface rupture and liquefaction points, it is found that the co-seismic groundwater level change is large in Chianan Plain, in the northwest area of the epicenter, and accompanied with a lot of ruptures and liquefactions located along the Hsinhua Fault. We compared the liquefaction points with the interpolated values of peak ground acceleration (PGA) and peak ground velocity (PGV) data, the result shows that the distribution of liquefaction points have the similar pattern with that of PGV values. The minimum threshold values of PGA and PGV for earthquake induced liquefaction are about 150 cm/s^2 and 40 cm/s, respectively. By the way, the observations in some wells in the deeper aquifer around the Hsinhua Fault show a different groundwater level change compared with the other wells in Chianan Plain. These wells show groundwater level decreases in the deep aquifer and increases in the shallow aquifer. In these wells, the Naba and Hsinhua wells show groundwater level convergence at different depths after the Meinong Earthquake. The earthquake enhances the connectivity between different aquifers and produces a vertical pressure propagation, that might be one possible mechanism for this phenomenon. The hypothesis of connectivity changes between different aquifers can be verified by analyzing the tidal response in different aquifers. Tidal analysis uses the phase shift pattern to judge if the aquifer permeability and transmissivity were changed after earthquakes, which is an important clue to understand how earthquake influences the hydrogeological properties. The results show that the pattern of phase shift at the Hsinhua well in different aquifers become similar, which is the evidence in proving the connection between different aquifers.
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