Possibilities to perform pre- and post-seismic groundwater chemical comparisons on regional groundwater flow systems are rare due to lack of data and observations. The Kumamoto earthquake provides an unusual opportunity to improve the knowledge on earthquake hydrology and earthquake effects on hydrochemistry of groundwater due to a wealth of pre- and post-quake observations. We analyzed 12 physiochemical parameters (SiO2, (NO3 – + NO2 –)-N, Fetotal, Mntotal, pH, F−, Cl−, SO4 2−, Na+, K+, Ca2+, and Mg2+) using self-organizing maps (SOM) combined with hydrological and geological characteristics to improve the understanding of changes in groundwater chemistry after a major earthquake. The results indicate that the earthquake induced hydrological and environmental change via fault forming (Suizenji fault systems), liquefaction, rock fracturing, and ground shaking. These geological processes created rock fresh reactive surfaces, rock loosening, and enhancement of hydraulic conductivity. In turn, this lead to secondary processes in groundwater chemistry by advection, dilution, and chemical reaction. The most obvious indicator of hydrological and environmental change was from the increased dissolved silica content stemming from fracturing and Si-O bond cleavage in silicate rocks. Besides this, decreasing concentration of common ions (Cl−, F−, Na+, K+, Ca2+) was found due to dilution from mountain-side water release. Increase in (NO3 – + NO2 –)-N, SO4 2−, and Mg2+ concentration occurred locally due to soil leaching of contaminants or agricultural fertilizers through surface ruptures in recharge areas. Increase of SO4 2− content also originated from leaching of marine clay in coastal areas and possibly sporadic deep crustal fluid upwelling. Increase in (NO3 – + NO2 –)-N and Cl− content occurred from sewage water pipe breaks in the Suizenji fault formation in urban areas. Decrease of pH occurred in a few wells due to mixing of river water and different types of aquifer groundwater. Increase of Fetotal and Mntotal concentration possibly originated from leaching of marine clay by liquefaction in coastal areas. However, in most cases the water chemistry changes were subtle, thus not resulting in any groundwater quality deterioration of water supplies. (Less)

中文翻译：

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2016年熊本地震影响的地下水化学时间特征使用自组织图

由于缺乏数据和观测，对区域地下水流系统进行地震前和地震后地下水化学比较的可能性很少。由于大量的震前和震后观测，熊本地震提供了一个不寻常的机会来提高地震水文学和地震对地下水水化学的影响的知识。我们使用自组织图谱 (SOM) 分析了 12 个理化参数（SiO2、(NO3 – + NO2 –)-N、Fetotal、Mntotal、pH、F−、Cl−、SO4 2−、Na+、K+、Ca2+ 和 Mg2+） ) 结合水文地质特征，提高对大地震后地下水化学变化的认识。结果表明，地震通过断层形成（水前寺断层系统）、液化、岩石破裂、和地面震动。这些地质过程创造了岩石新鲜的反应面、岩石松动和水力传导率的增强。反过来，这通过对流、稀释和化学反应导致地下水化学的二次过程。水文和环境变化的最明显指标是由于硅酸盐岩中的压裂和 Si-O 键断裂引起的溶解二氧化硅含量增加。除此之外，由于山侧水释放的稀释，发现常见离子（Cl-、F-、Na+、K+、Ca2+）的浓度降低。(NO3 – + NO2 –)-N、SO4 2- 和 Mg2+ 浓度的增加发生在局部，原因是土壤通过补给区的地表破裂渗滤污染物或农业肥料。SO4 2− 含量的增加也源于沿海地区海相粘土的淋溶和可能是零星的深部地壳流体上涌。(NO3 – + NO2 –)-N 和 Cl- 含量增加是由于城市地区水前寺断层地层的污水管道破裂引起的。由于河水和不同类型的含水层地下水混合，一些井的pH值下降。Fetotal 和Mntotal 浓度的增加可能源于沿海地区液化对海相粘土的浸出。然而，在大多数情况下，水化学变化是微妙的，因此不会导致供水的任何地下水质量恶化。（较少的）由于河水和不同类型的含水层地下水混合，一些井的pH值下降。Fetotal 和Mntotal 浓度的增加可能源于沿海地区液化对海相粘土的浸出。然而，在大多数情况下，水化学变化是微妙的，因此不会导致供水的任何地下水质量恶化。（较少的）由于河水和不同类型的含水层地下水混合，一些井的pH值下降。Fetotal 和Mntotal 浓度的增加可能源于沿海地区液化对海相粘土的浸出。然而，在大多数情况下，水化学变化是微妙的，因此不会导致供水的任何地下水质量恶化。（较少的）