2022年1月8日门源M6.9地震前青海地区逸出气氡异常特征分析

Anomaly characteristics of radon in escape gas in Qinghai area before Menyuan M6.9 earthquake on January 8,2022

2022年1月8日青海省海北州门源县发生M6.9地震,震前青海地区出现两项逸出气氡异常(西宁、乐都)。以此为研究对象,利用流体地球化学方法,进行异常特征分析研究。TDS范围:西宁采样点为9084.3~11316 mg/L;乐都采样点为897.01~989.26 mg/L。水化学类型为Na-SO_(4)、Na-Cl,均显示水-岩反应程度较弱。SO^(2-)_(4)、HCO^(-)_(3)浓度发生较明显变化,指示异常出现前及异常持续过程中有地下水循环径流途径较短的低矿化水混入,计算热储温度与循环深度,显示出深部水体交换不明显的特征。地震孕育时,区域应力加载导致周围岩石产生裂隙及孔隙,从而导致地球物理场的氡值变化,同一时段的水岩反应加剧,使得水化学离子组分浓度亦发生相应变化,结合氡值异常机理及历史震例研究,分析认为该异常是可信的地震前兆异常,对祁连带6级以上地震有较好的指示意义。

An M6.9 earthquake occurred in Menyuan County,Qinghai Province on January 8,2022.There were anomalies of radon in the escape gas in Xining and Ledu of Qinghai Province before the earthquake.This paper focused on the abnormal characteristics by using the fluid geochemical method.The results showed that the total dissolved solids(TDS)of sampling point in Xining ranged from 9084.3 to 11316 mg/L,and that in Ledu ranged from 897.01 to 989.26 mg/L.The hydrochemical types are Na-SO_(4)and Na-Cl,showing that the degree of water-rock reaction is weak.The concentration of SO^(2-)_(4)and HCO^(-)_(3) changed significantly,indicating that low mineralized water with short groundwater runoff was mixed before and during the anomalies.The calculation results of heat storage temperature and circulation depth showed that the exchange of deep water body was not obvious.During the preparation of an earthquake,the regional stress loading leads to the formation of cracks and pores in surrounding rocks,resulting in the change of radon value in the geophysical field.The water-rock reaction increases in the same period,resulting in the corresponding change of hydrochemical ion concentration.Combined with the abnormal mechanism of radon value and the study of historical earthquake events,the anomalies are suggested to be credible earthquake precursor anomalies,which have a good indicating significance for M≥6 earthquakes in the Qilian seismic belt.