Abstract Large earthquakes change the hydrogeological properties of aquifer systems, such as permeability, and cause changes that impact groundwater flow. To understand these changes in mountain aquifer systems, we analyzed stable isotopic ratios of water molecular (δD and δ18O) of H2O and chlorofluorocarbons (CFCs) concentrations of natural spring waters and compared these values between before (2009) and after (2017) the 2016 Kumamoto crustal earthquake sequence in Kumamoto-Aso area, southern Japan. Stable isotope ratios were used to identify the spring source characteristics that reflected recharge elevations, whereas CFC age tracers were applied to evaluate the contribution of earthquake-induced additional waters from different pathways (shorter or longer) and/or CFC-enriched (contaminated) surface waters. In general, spring waters after the earthquake became more depleted in water isotopic compositions than those before the earthquake, suggesting an increased contribution of waters recharged from higher elevations across the area. In addition, changes observed in CFC-12 concentrations were classified into several increasing/decreasing patterns defined by the contribution of additional waters from different flow paths, such as older groundwater with longer flow paths, younger groundwater from shorter flow paths, and CFC-enriched (contaminated) water released from shallow aquifers and soils. These isotopic and chemical features, when combined with previously documented seismotectonic surface rupture distributions, demonstrated the occurrence of coseismic mountain water release due to enhanced permeability. These findings enabled us to document how groundwater flow changes in mountain aquifers. Although CFC age markers have rarely been applied as a tool to investigate coseismic hydrological changes, our study exemplifies their usefulness—in combination with stable isotope ratios—in such investigations.

中文翻译：

---

天然泉水稳定同位素和CFC-12成分推断2016年7.0级熊本地震后地下水流系变化

摘要 大地震会改变含水层系统的水文地质特性，例如渗透率，并引起影响地下水流动的变化。为了了解山区含水层系统的这些变化，我们分析了天然泉水中 H2O 和氯氟烃 (CFC) 浓度的水分子（δD 和 δ18O）的稳定同位素比率，并比较了 2016 年之前（2009 年）和之后（2017 年）的这些值日本南部熊本阿苏地区的熊本地壳地震序列。稳定同位素比率用于识别反映补给高度的泉源特征，而 CFC 年龄示踪剂用于评估来自不同路径（较短或较长）和/或富含 CFC（污染）表面的地震引起的额外水的贡献水域。一般来说，地震后泉水的水同位素组成比地震前更加枯竭，这表明该地区较高海拔的水补给的贡献增加。此外，观察到的 CFC-12 浓度变化分为几种增加/减少模式，这些模式由来自不同流动路径的额外水的贡献定义，例如流动路径较长的老地下水、较短流动路径的较年轻地下水和富含 CFC 的地下水。从浅层含水层和土壤释放的（受污染的）水。这些同位素和化学特征与先前记录的地震构造表面破裂分布相结合，证明了由于渗透性增强而发生的同震山区水释放。这些发现使我们能够记录山区含水层中地下水流量的变化。尽管 CFC 年龄标记很少被用作调查同震水文变化的工具，但我们的研究证明了它们在此类调查中的用处——结合稳定同位素比率。