Geochemical Characteristics Of The Wells And Springs For Seismic Monitoring Sites In Southeastern Liaoning Province

Concerrations of ions(Li⁺,Na⁺,K⁺,Ca²⁺,Mg²⁺,F^-,Cl^-,Br^-,SO₄^2-,NO₃^-,HCO₃^-and CO₃^2-)and hydrogen and oxygen isotopes(?D and?¹⁸O)of 95 water samples,which were collected from10 wells and springs at the seismic observation sites in Liaoning Province during May to December2015,August 2016,October 2017 and August 2018,were measured in order to investigate the geochemical bankground and origins of the underground waters and correlate the geohydrochemical variations with the earthquakes.The geochemical bankground and origins of the underground waters as well as geohydrochemical correlation with earthquake were investigated based on concerrations of ions(Li⁺,Na⁺,K⁺,Ca²⁺,Mg²⁺,F^-,Cl^-,Br^-,SO₄^2-,NO₃^-,HCO₃^-and CO₃^2-)and hydrogen and oxygen isotopes(?D and?¹⁸O)of 95 water samples that were collected 11 times from 10 wells and springs at the seismic observation sites in Liaoning Province during May to December 2015,August 2016,October 2017 and August 2018.The measurements show that the water temperature and total dissolved solids(TDS)of the water samples were in the ranges of 12.7?60.3?and 89.88?1120.59 mg/L,respectively.According to the Shukarev's classification,the groundwaters are divided into 10 types:Na·Ca-HCO₃,Na-HCO₃,Na-HCO₃·SO₄,Na-SO₄·HCO₃,Ca·Na-HCO₃,Ca·Mg·Na-HCO₃,Ca·Na·Mg-HCO₃,Ca-SO₄·HCO₃,Ca·Mg-HCO₃ and Ca·Mg-Cl.The?D and?¹⁸O values of the water samples were ploted along the local atmospheric line,indicating that the waters were mainly derived from atmospheric precipitation with a small amount of deep fluid.A few points showing slight oxygen drift indicated the water-rock reaction in the deep cycle process of groundwater and the mixiture of deep source water.There characteristics of geochemical characteristics of the groundwaters and temperatures of geothermal reservoirs differentiated obviously site to site in the study region.The recharge elevations of groundwaters were estimated in a range from 1380 to 2080 m.Compared with the actual topography,the recharge area of groundwaters is the Changbai Mountains in the east Liaoning Province.Meteoric precipitation evolved into Na-HCO₃,Na-HCO₃,Na-HCO₃·SO₄ types of waters with high F^-content resulted from water-rock interaction occurred in the granite distribution area,showing a typical feature of granite fracture water.The Ca-SO₄·HCO₃ water was mainly affected by carbonate dissolution and oxidation of sulphide.The water samples of Beiguanquan(BGQ)are affected by carbonate rocks strata and seawater intrusion to form Ca·Mg-Cl type water.The hydrolysis of feldspar and ion exchange of clay minerals in Tertiary glutenite resulted in the relative enrichment of Na⁺and Ca²⁺to form Na·Ca-HCO₃ type and Ca·Mg-HCO₃type water,which were affected by the dissolution of carbonate rocks and sodium bearing silicates.Values of?(Ca²⁺+Mg²⁺)/?(HCO₃^-+SO₄^2-)of the water samples were close to 1,indicating that the groundwater mainly came from the dissolution of sulfate and carbonate minerals in the run off process.The?Na⁺/?Cl^-ratios of the water samples varied slightly,which is more suitable for the extraction of geochemical anomaly information.During the sampling period,there were 7 earthquakes of magnitude 4 or above occurred the Haicheng concealed fault zone,Chaoyang fault zone and Tanlu fault Liaodong Bay section in the study area,mainly in the Haicheng-Gaizhou-Dashiqiao and Chaoyang areas,as well as near Shandong sea area On the concealed fault zone,the epicenter distance of all sampling points is within the range of 20?300 km.During a period of time before and after the earthquake,some springs/wells showed abnormal changes in the concentration of K⁺,F^-and Cl^-ions,which may be caused by the mixing of deep fluids into shallow groundwater.The changes in the concentration of K⁺,Mg²⁺,Ca²⁺,and Cl^-ions respond well to earthquakes in Liaoning.The sampling points of Anbo,Xujiapu,Dijiapu,Tangchi,and Fengcheng had significant abnormal increases before the earthquake and their responses were sensitive.The overall water quality in the study area is poor.The groundwater quality of Dijiapu(DJP),Fengcheng(FC),Liaoyang(LY),Panjin(PJ),and Xujiapu(XJP)sampling points have changed greatly.Due to the reaction or the mixing of deep fluids,some ionic components of each sampling point have changed,leading to changes in water quality.The research results can be used for fluid geochemical seismic monitoring,prediction and water environment research in Liaoning area.