九江地震台观测井水氢氧同位素特征及意义

Hydrogen and Oxygen Isotope Characteristics and Significance of Groundwater from Jiujiang Seismic Station

摘要:

在地震地下流体观测研究中，基于氢氧同位素示踪技术研究地下水补给源及循环过程是常用的技术方法之一。本文给出了九江地震台2号观测井水、大气降水、周边水库水及高山泉水等样品的氢氧同位素测定结果，表明地下水δ¹⁸O测值介于-7.59‰~-6.09‰，平均值-6.99‰，δD测值介于-45.22‰~-39.69‰，平均值-42.32‰，变异异数分别为0.09、0.16；大气降水δ¹⁸O测值介于-13.00‰~-1.27‰，平均值-4.74‰，δD测值介于-96.13‰~-4.74‰，平均值-46.87‰，变异异数分别为0.40、0.56，与降水相比，地下水氢氧同位素变化更为稳定。大气降水氢氧同位素2017年5~10月表现为明显的降水效应，2018年11~4月表现为明显的温度效应，而地下水氢氧同位素并未表现出明显的降水效应和温度效应。氢氧同位素及过量氘揭示地下水在下渗补给前经历了明显的蒸发分馏作用，并与围岩进行¹⁸O交换，δ¹⁸O与δD计算得出的补给高程分别约为647、440m。九江台观测井的观测层地下水为大气降水成因的构造裂隙水，属于大气成因型且循环过程为较稳定的裂隙水补给并形成承压自流井。

Abstract:

In the study of underground fluids in earthquakes,groundwater recharge and circulation are one of the important research contents. Hydrogen and oxygen isotope tracing technology is one of the most commonly used methods in studying the process. By means of the hydrogen and oxygen isotope determination,we analyze the samples from the groundwater in Well No.2 of the Jiujiang Seismic Station,atmospheric precipitation,the water flowing from the surrounding Tianhuajing Reservoir and a kind of alpine spring water named Mawei Water. The results show that groundwater δ¹⁸O is between -7.59‰ and -6.09‰ and average value is -6.99‰ and that its δD is from -45.22‰ to -39.69‰ and average value-42.32‰. At the same time,the coefficient of variance is separately 0.09 and 0.16. As for the atmospheric precipitation,its atmospheric precipitation ranges from -13.00‰ to -1.27‰ and average value-4.74‰,compared with the average value-46.87‰,δD changes between 96.13‰ and -4.74‰ with 0.40 and 0.56 as coefficient of variance. Obviously,hydrogen and oxygen isotope of groundwater changes more stably than precipitation's. The hydrogen and oxygen isotope of atmospheric precipitation is reflected by obvious precipitation effect in the summer half year,while the temperature effect in the winter half year is not obvious. The hydrogen and oxygen isotope of groundwater has no significant effects on precipitation and temperature. Hydrogen and oxygen isotope and excess enthalpy reveal that groundwater experienced evaporation fractionation before infiltration replenishment and exchanged with surrounding rocks totally in ¹⁸O. The recharge elevations calculated by δ¹⁸O and δD are about 647m and 440m respectively. Generally speaking,the groundwater in the Jiujiang seismic station belongs to a type of atmospheric origin,and its circulation process is a pressure-bearing artesian well formed by the supplement of a relatively stable fissure water.