Insight into groundwater quality change before and after the 2016 Kumamoto earthquake
Nahoko Hamada1, Hitomi Koga1, Kimio Katsuya1
1Kumamoto Groundwater Foundation, 8-16 Anseimachi, Chuo-ku, Kumamoto-shi 860-0801, Japan.
The Science of the Total Environment
|December 3, 2024
Summary
The 2016 Kumamoto Earthquake significantly altered groundwater quality for many wells, with changes persisting for years. The aquifer breaching/fluid mixing model likely explains these seismic impacts on drinking water resources.
Area of Science:
- Geochemistry
- Environmental Science
- Hydrogeology
Background:
- Groundwater is the sole drinking water source for 100% of the Kumamoto population.
- Earthquakes can impact groundwater quality, but data is often limited.
- Six years of monthly monitoring data (since 2014) provide a robust dataset.
Purpose of the Study:
- To statistically evaluate groundwater quality changes after the 2016 Kumamoto Earthquake.
- To investigate the mechanisms driving these water quality alterations.
- To assess the long-term stability of observed changes.
Main Methods:
- Analysis of major ionic components using Stiff diagrams.
- Application of k-medoids clustering for statistical analysis of water quality data.
- Evaluation of temporal trends and spatial relationships of water quality changes.
Main Results:
- Stiff diagrams showed no overall change, but k-medoids identified significant shifts in 11 out of 14 samples.
- Water quality changes were persistent, not temporal, lasting over four years post-earthquake.
- Individual parameter changes varied by site; nitrate fluctuations were linked to precipitation.
Conclusions:
- The aquifer breaching/fluid mixing (AB/FM) model is the most probable explanation for groundwater quality changes.
- Seismic shaking likely altered water pathways, leading to the observed hydrochemical shifts.
- Understanding these mechanisms is crucial for managing drinking water resources post-seismic events.
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