The Hydrogeochemical Seismic Precursory Anormal Characteristics Of Hot Springs In Ning-er Tong-guan Volcanic Area

The monitoring of hydrogeochemical characteristics provides precursory information of seismic activities.In this study,eight hot spring sites in Ning er Tong guan,Yun nan province were selected for sampling and analysis,to discuss the connection between earthquake and hydrogeochemical factors.The results are as follows:(1)Tong guan volcanic hot springs include six hydrogeochemical types: Na·Ca-HCO3,Na·Cl-HCO3,Na-HCO3,Ca-HCO3,Na·Ca-SO4·HCO3 and Na·CaCl·SO4;(2)The oxygen and hydrogen isotopes(δ18O and δD)range from 12.69 to-10.80‰ and-89.2 to-81.5‰ respectively,which indicates the main source of the recharge for the hot springs is precipitation,and the recharge elevation ranges from 2.0 to 2.7km;(3)The geothermal reservoir temperature of hot springs,calculated by Si O2 hydrogeochemical temperature scale,range from 52.5 to 56.4℃.The circulation depth of hot springs was estimated to be around 1.1 to 1.3km.The main source of heat is from geothermal gradient and magma hot;(4)Before 2020-7-12 Lu Chun,Yunnan earthquake,The concentration of Na+、Cl-、SO42-in QP and XS hot spring rise synchronously.The Na+、Cl-、SO42-ions response in three continuous monitoring sites were noticeable while 2021-6-10 Shuang bai earthquake.Concentration of These ions rose 5-10 days before earthquakes,then decreased to average levels.The anormal extent relates to the distance of epicenter and earthquake magnitude;(5)The main explanation of anomalies is that variation of tectonic stress field results in the change of circulation of groundwater through fractures,and then mixing the pore water of the faults into the groundwater,therefore changing the compositions of hot spring water.