Changes of groundwater flow systems after the 2016 Mw 7.0 Kumamoto earthquake deduced by stable isotopic and CFC-12 compositions of natural springs

Kiyoshi Ide, Takahiro Hosono, Makoto Kagabu, Keisuke Fukamizu, Takahiro Tokunaga, Jun Shimada

研究成果: Article査読

11 被引用数 (Scopus)

抄録

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.

本文言語English
論文番号124551
ジャーナルJournal of Hydrology
583
DOI
出版ステータスPublished - 2020 4月
外部発表はい

ASJC Scopus subject areas

  • 水の科学と技術

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