Hydrogeochemistry Of The Hot Springs In Western Sichuan Province, Southwestern China After The Wenchuan M_s8.0Earthquake

Hydrogeochemistry of120water samples from32hot springs in the western Sichuan Province after the Wenchuan Ms8.0earthquake was investigated by analyzing the concentrations of cation(K+, Na+, Ca2+and Mg2+), anion(Cl-, SO42-, HCO3-and CO32-) and the isotopic compositions of hydrogen and oxygen (δD and δ18O). The water samples of the hot springs were collected four times in June2008, October2008, June2009and April2010. Hydrogeochemical data indicated the spring waters can be classified into9chemical types:Na(Ca)-HCO3(SO4), Na(Mg)-HCO3(SO4), Ca(Na)-HCO3(SO4), Mg(Ca)-SO4, Ca(Mg)-SO4, Ca(Mg)-HCO3, Mg (Ca)-HCO3, Na-Cl (HCO3) and Ca(Na)-SO4(HCO3). The values of δD and δ18O of the120water samples were plotted along the local meteoric water line with different extent shifts in the diagram of δD vs δ18O, which indicated that the spring waters were mainly originated from meteoric water and with different extent alteration. Attributed to water-rock interaction and mixture of deep fluids, the geochemical characteristics and the temperatures of the geothermal reservoir showed spatial differences. The values of δD and δ18O for the water samples of the springs nos.10-25from the higher mountain area were more negative, but the temperatures, TDS and Cl-of the springs were higher, which may result from the contribution of condensated water of deep vapor. Concentrations of K+and SO42-of the water samples of the Guanding Spring, Longtougou Spring and Erdaoqiao Spring in the Kangding district exhibited evident increases before the mainshock, with the amplitude ranging from19.3%to59.6%, indicating more supplement of deep fluids enriched in K+and SO42-under the increase of tectonic stress during the before the Wenchuan earthquake. Most of the aftershocks occurred in the Longmenshan fault zone, and more than80%occurred two months before and after the first sampling. The chemical and isotopic variations of the water samples nos.1-5from the Longmenshan fault zone closer to the epicenter area more obviously decreased after the mainshock, with the chemical parameters of the water samples collected in October2008by some23%to95%, and the δD-δ18O plots approached the local meteoric water line after sizeable shift in June2008, indicating less supplement of deep fluids under the stress adjustment. For the water samples from other fault zones, the amplitudes of the chemical variations were less than10%, and no marked changes for the δD and δ18O were observed. Na+, HCO3-and TDS of the water sample from Bamei Spring in the Xianshuihe fault zone increased obviously, with the amplitudes of53%,38%and38%respectively on17April,2010, which may be related to the Ms5.4event of28April,2010with an epicenter distance of15km.