河套盆地周缘泉水化学组分对2015年4月15日阿左旗MS5.8地震的响应*

根据河套盆地周缘断裂带泉水的氢、氧同位素组成和水化学组分,讨论了该区地下水的化学类型、成因及其与地震活动的关系。于2014年9月下旬和2015年4月15日M_S5.8阿左旗地震震后在河套盆地周缘的乌拉山断裂带、色尔腾断裂带、狼山断裂带以及桌子山断裂带采集了17个泉水和井水样品,测得水样的TDS分布在143.8~42 553.0mg/L范围内,δD和δ¹⁸O值分别在-83.6‰~66.56‰和-11.16‰~8.2‰的范围内,来源为大气降水。根据舒卡列夫分类法,震前水样可划分为13种水化学类型,震后西山咀、圐圙朴隆等5个点采样点泉水的水化学类型发生变化。其中,乌拉山断裂带的水样以HCO₃-Ca型低矿化度地表水为主;色尔腾断裂带、狼山断裂带泉水受白垩系含水层影响,矿化度较高,富含HCO^-₃及SO^2-₄;桌子山一带受煤矿开采影响,水样以富SO^2-₄和Cl^-的高矿化度水为特征。地震前后TDS、阴、阳离子以及γNa/γCl、γ(SO₄+Cl)/γHCO₃、γHCO₃/γCl等毫克当量比值能够较好地反映地震。2015年4月15日阿左旗M_S5.8地震后,呼鲁斯太、迪延阿贵庙及八一井的水化学组成变化较大,对地震响应较为敏感。呼鲁斯太地区泉水的TDS稍有降低,但HCO^-₃在阴离子中所占比例有所增加,表明震后该地区含水层的泉水与较低矿化度的含碳酸盐岩含水层水发生了混合;八一井的TDS值有所增加,γNa/γCl比值有所降低,表明深部高矿化度水的混入;迪延阿贵庙水样的TDS稍有下降,但NaCl的相对含量较震前有所升高,表明有低矿化度NaCl水的混入。本工作不仅确定了该区水文地球化学背景,而且对地震监测和预测具有一定参考价值。

Hydrochemcal Response of Hot Springs around Hetao Basin to the 15April 2015 MS5.8Alxazuoqi Earthquake

Hydrochemical variations caused by the 15April 2015 MS5.8Alxazuoq earthquake were discussied based on the ratios of hydrogen and oxygen isotopes and ion concentrations of the spring waters from the fault zones around the Hetao basin in western Inner Mongolia.17water samples were collected from the springs and wells in the Wulashan fault zone,Serteng fault zone,Langshan fault zone and Zhuozishan fault zone.The hydrochemical data attained indicated that the TDSvalues of the waters ranged from 143.8to 42553.0mg/L,which can be classified into 12chemical types using the Schukalev hydrochemical classification method.The water samples in the Wulashan fault zone were characterized by low TDS and Ca-HCO₃ type,showing an origin of atmospheric precipitation. The waters in the Seerteng and Langshan fault zones were enriched in HCO^-₃ and SO^2-₄with higher TDS,resulting from water-rock reaction in Cretuceous aquifer.The waters collected from the Zhuozishan fault zone were characterized by higher TDSand enrichment of SO^2-₄ and Cl^-,caused by mixing water with coal bed.Values ofδD andδ¹⁸O ranged from -83.6‰to 66.56‰ and-11.16‰to 8.2‰,respectively,indicating the waters were mainly meteoric origin.Ratios of ion concentrations between the samples of 2015and the samples of 2015as well as milliequivalent ratio,such asγ(Na+K)/γCl,γ(SO⁴+Cl)/ γHCO₃,γHCO₃/γCl,can better reflect the earthquake activity.After the April 15,2015 MS5.8Alxazuoqi earthquake,the TDS values of the waters in the Hulusitai and Diyanaguimiao areas shown a slight decrease trend while the proportion of HCO^-₃ in anion increased,which might result from mixture of low TDS water in the shallow aquifer. However,TDSvalue of the water(S12)from the deep well increased obviously and the ratio ofγ(Na+K)/γCl decreased,indicating mixing of higher TDS water from the deep strata.The results provide a hydrochemical background of the study area and are in favor of seismic monitoring and forecasting.