Significant changes in groundwater systems were observed after the 2017 M_w 5.5 Pohang earthquake. Groundwater level changes cannot be explained solely by poroelastic responses to the earthquake. In this study, we analyzed hydrogeochemical data, including environmental isotopes (¹⁸O, ²H, ⁸⁷Sr/⁸⁶Sr, and ²²²Rn) of water samples as well as time‐series data of groundwater level, temperature, and electrical conductivity. Principal component analysis (PCA) and physical modeling of pore pressure changes were also used. Some anomalies in time‐series data could be explained by the distributions of pore pressure changes based on modeling. However, the other wells, which did not have the correlation between time‐series data and modeling results, exhibited abnormal patterns in hydrogeochemical and isotope data. Stiff diagrams showed differing patterns of temporal change among groundwater wells. These diagrams and isotopic anomalies revealed possible mechanisms underlying the aftereffects of earthquakes, including saline water mixing, water‐rock interactions, deep fluid upwelling, and bedrock fracture opening. These anomalous phenomena were related to the clusters derived by PCA and depended on the distance to the epicenter, faults, and sea water. This study highlights that a single measurement is insufficient to reliably interpret groundwater responses, whereas a combined hydrogeochemical and physical interpretation may provide critical information for clarifying anomalies related to earthquakes.

中文翻译：

---

应对2017年韩国浦项5.5兆瓦地震的地震异常的水文地球化学证据

2017年后，观察到地下水系统显著变化中号_W¯¯ 5.5浦项地震。不能仅通过对地震的孔隙弹性响应来解释地下水位的变化。在这项研究中，我们分析了水文地球化学数据，包括环境同位素（¹⁸ O，² H，⁸⁷ Sr / ⁸⁶ Sr和²²²水样本的Rn）以及地下水位，温度和电导率的时间序列数据。还使用了主成分分析（PCA）和孔隙压力变化的物理模型。时间序列数据中的某些异常现象可以通过基于建模的孔隙压力变化分布来解释。但是，其他时间序列数据与建模结果之间没有关联的井在水文地球化学和同位素数据中表现出异常模式。刚度图显示了地下水井之间时间变化的不同模式。这些图和同位素异常揭示了地震后效的潜在机制，包括盐水混合，水-岩相互作用，深部流体上升和基岩裂缝张开。这些异常现象与PCA产生的星团有关，并取决于距震中，断层和海水的距离。这项研究强调，单项测量不足以可靠地解释地下水响应，而水文地球化学和物理解释相结合可能为澄清与地震有关的异常现象提供关键信息。