[A-HW24] 熊本地震に伴う地表水と地下水の変化

[AHW24-P07] 微量元素濃度組成と金属元素同位体比からみた熊本地域地下水の地域的特徴と熊本地震による影響評価

杉本 直人¹、*谷水 雅治¹、細野 高啓² (1.関西学院大学、2.熊本大学大学院先導機構)

キーワード：地下水、同位体

In these last few decades, isotopic traces have been used to understand the origin and flow of groundwater. In this study, we analyzed various isotopes from groundwater samples in Kumamoto area, Japan. Groundwater in this area is supplied from Mt, Aso, and utilized as a main source of water supply in Kumamoto City. Its recharge by meteoric water is the main source as indicated by conventional delta-¹⁸O and delta-D isotopes of water, but additional inputs from different sources are suggested. In this study we tried to detect the presence of additional sources using delta-¹¹B and delta-⁷Li isotope ratios dissolved in water as well as concentrations of B, Li, and major dissolved ions, and D/H-¹⁸O/¹⁶O values of H₂O. B and Li are conservative trace elements in typical groundwater system (pH, Eh, EC), and these isotopes have very wide variations(0-30 permil) in nature owing to its relative large mass differences. Stagnant groundwater and thermal fluids tend to have low delta-values and seawater has high values, so the isotope systematics are useful to estimate origin of groundwater.