Geochemistry and Dissolved Gases Variation of Artesian Well in Active Fault Zone, SW Taiwan

• Main Authors: Chun-Wei Lai, 賴俊瑋
• Other Authors: Tsanyao F. Yang
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/30175888185952360939

碩士 === 國立臺灣大學 === 地質科學研究所 === 104 === Several studies have proposed that micro-fracturing prior to major seismic events may be responsible for changes of the groundwater chemistry. Precursory changes in groundwater chemistry are often attributed to the new fractures, the opening of pre-existing micro-fractures or the destruction of hydrologic barriers. It is believed that isolated aquifers may have chances to subsequently mix together and trapped gases in the rock matrix can escape when subjected to earthquake activities. The aim of this study is to probe into the probable mechanism of geochemical variations of groundwater that plays in an earthquake cycle bying the data collected from the Yunshui dissolved gases and groundwater monitoring station during the year of 2014. Dissolved ions Na、K、Ca、Mg、HCO3、Cl、SO4, stable isotope C、H、O, dissolved gases CH4、N2、O2、Ar、CO2 and dissolved radon were measured with the multi-monitoring system. Results show that the chloride and dissolved methane concentrations of groundwater have two anomalies around July 12 and September 18. However, no immediate corresponding earthquake has been detected at the Yunshui station. By using earthquake activity function from calculating the annual earthquakes, the anomalies were found to emerge with a time delay of more than 2 months. It could be attributed to non-existence of a high pressure fluids pathway. The anomalies have the property of fast recovery. It is suggested that the source of anomalies is the trapped fluids of the host rock. The fluid of of Yunshui Artesian Well is mainly formation water, which is a mixture of the ancient sea water and the small amount of meteoric water. The Na/Cl ratio of Yunshui groundwater is 0.94, higher than the average seawater value of 0.85. The geochemical characteristics inferred that the extra Na in groundwater probably resulted from ion exchange. It also support that the importance of the host rock in aquifer.