Experimental Study On The Genetic Mechanism Of Chemical Anomalies In Seismic Groundwater

Earthquake prediction is a huge and realistic demand of human beings.a large number of monitoring data show obvious fluid geochemical anomalies before and after the earthquake.however,the relationship between fluid anomalies and seismicity is not clear at this stage.Therefore,understanding the formation mechanism of seismic fluid geochemical anomalies is of great significance for earthquake monitoring and prediction.Water-rock reaction experiment,which can simulate the subsurface temperature and pressure environment,is an effective way to study the formation mechanisms of hydro-chemical anomalies connected with the earthquake.This paper,focused on the issues such as the causes of the abnormal changes in ion concentrations before and after the earthquake and the formation mechanisms,and with the water-rock reactions of different rocks(limestone,peridotite,and granite)under different conditions(temperature,particle size,and time)as the study object,studied the changes of Na⁺,K⁺,Cl^-,SO,Ca²⁺,and Mg²⁺in the solutions after the reactions using the controlled variables and partial least squares.Coupled with hydro-chemical observation data from seismic stations,the results obtained show that with the increase of time,Na⁺,K⁺and SO increased to 1.56,1.48,2.09 times of the initial concentration respectively;Na⁺,K⁺increased to 3.63,2.13 times of the initial concentration.with the increase of temperature,and Na⁺,K⁺,Cl^-and SO increased to 7.15,4.80,4.75,2.66 times of the initial concentration with the decrease of particle size.In the peridotite water-rock reaction,Na⁺,K⁺and SO increased to 1.56,1.29,1.51 times of the initial concentration respectively with the increase of reaction time,Na⁺,K⁺and SO increased to 4.68,1.43,2.12 times of the initial concentration with the increase of temperature,and Na⁺,K⁺and SO increased to 9.58,4.31,6.22 times of the initial concentration with the decrease of particle size.In the water-rock reaction of granite,Na⁺,K⁺and SO increased to 1.68,2.31,1.83times of the initial concentration respectively with the increase of time,Na⁺,K⁺increased to 2.45,2.36 times of the initial concentration with the increase of temperature,and Na⁺,K⁺and SO increased to 4.32,3.10,3.3 times of the initial concentration with the decrease of particle size.The effect of particle size on the ion concentration of solution is very obvious.with the decrease of particle size,the contact area between rock and water increases,and the ion concentration of Na⁺,K⁺,Cl^-and SO increases obviously.The results indicate that the contact area of the water-rock reaction is the main factor affecting the ion concentrations.Therefore,the rupture of water-bearing rock formation under the action of tectonic stress,resulting in the change of water-rock reaction contact area,may be one of the important formation mechanisms for the short impending hydro-chemical anomaly before and after the earthquake.