| China is most severely affected by earthquake hazards. The trends of earthquake activity in the northern part of north-south seismic zone become more and more intense after the MS8.0 Wenchuan earthquake. For instance, the MS5.8 Alxa Zuoqi earthquake occurred in 15 April 2015. The Hetao basin and vicinity was considered as an imprortant region for earthquake mornitoring in the 2015~2025 block map of seismic risk. Sofar, the comprehensive research of hydrochemistry in the Hetao basin and vicinity is rarely reported. Therefore, it is necessary to investigate the geochemical features of groundwaters in the region, in order to enhance hydrochemical mornitoring for earthquake, obtain the precursors of earthquake and mitigate the seismic hazards.The hydrochemical type, origin of the groundwaters and chemical variations caused by the 15 April 2015 MS 5.8 Alxa Zuoqi earthquake, as well as water quality assesment were discussed based on the isotopic ratios of hydrogen and oxygen, ion concentrations of the spring(well) waters from the fault zones around the Hetao basin in western Inner Mongolia. 88 water samples were collected from 28 springs and wells in the Wulashan fault zone, Serteng fault zone, Langshan fault zone and Zhuozishan fault zone in 24 ~ 27 September 2014, 16 April and 17 ~ 23 November 2015 and 2 ~ 7 March 2016.The isotopic compositions of H and O were measured with a L1102-I type of a Picarro Isotopic Water Analyzer, the values of δ18O and δD are with the errors of 0.1‰ and 0.5‰ respectively. Concentrations of conventional ions were analyzed with an ICS-900 type of Ion Chromatograph and conecentrations of trace elements with a Perkin Elmer Optima 8000 type of Inductively Coupled Plasma Optical Emission Spectrometry(ICP-OES).The values of δD and δ18O of the water samples range from-83.6‰ ~ 36.0‰ and﹣11.7‰ ~-1.2‰ respectively, which scattered along the global meteoric water line, indicating a meteoric origin of the waters.The hydrochemical types in the study area are complex, showing a tedence of increase SO42- of concentration from east to west. The samples from the Wulashan fault zone were characterized by low TDS and Ca-HCO3 type, showing an origin of atmospheric precipitation. The waters in the Serteng fault zones were enriched in HCO3- and SO42- with higher TDS, which can be attributed to water-rock reaction in Cretuceous aquifer. The underground water characterized by HCO3- and SO42- in Langshan area is controlled by the Proterozoic aquifer and the endogenous sulfide deposit. The water collected from the Zhuozishan fault zone were characterized by higher TDS and enrichment of SO42- and Cl-, which can be caused by mixing water with coal mine.After the 15 April 2015 MS5.8 Alxa Zuoqi earthquake, the hydrochemical compositions of Hulusitai, Bayijing, Qianligou and Diyanagui varied significantly, which can indicated the mixture of defferent waters.The concentrations of most trace elements(such as Be, Cd, Co, Cu, Ni, Pb, Sb) were less than the detection limits. The samples from Xiliushu, Jinshan, Baga, Qianligou had higher concentrations of Fe, Mn, Al than other samples, which may be attributed to polymetallic sulfide deposit and coal mine. The other trace elements have a low concentrations owing to various factors.The water qualities are devided into five levels according to “The Ground Water Quality Standard”—GB/T14848-1993. The waters samples collected in 2 ~ 7 March 2016 were assesd by the F-score method. The assessment results indicated that 7 of 25 water samples belonged to the level II, 9 to the level IV and 9 to the level V, which indicates most waters are not suitable for drinking purpose except the spring waters in Dahuabei, Hailiutu, Yangguang, Aguimiao, Diyanaguimiao, Xiliushu, Lingwudaquan. |
PDF Full Text Request