Temporal characteristics of groundwater chemistry affected by the 2016 Kumamoto earthquake using self-organizing maps
Nakagawa, Kei LU
; Yu, Zhi Qiang
; Berndtsson, Ronny
LU
and Hosono, Takahiro
(2020)
In Journal of Hydrology
582.
- Abstract
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... (More)
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)
- author
- Nakagawa, Kei
LU
; Yu, Zhi Qiang
; Berndtsson, Ronny
LU
and Hosono, Takahiro
- organization
- publishing date
- 2020
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Earthquake hydrology, Groundwater geochemistry, Kumamoto earthquake, Self-organizing maps
- in
- Journal of Hydrology
- volume
- 582
- article number
- 124519
- publisher
- Elsevier
- external identifiers
-
- scopus:85077803874
- ISSN
- 0022-1694
- DOI
- 10.1016/j.jhydrol.2019.124519
- language
- English
- LU publication?
- yes
- id
- f80d7ec8-2cfa-4bda-b2af-105bd75e04c5
- date added to LUP
- 2020-01-23 12:11:01
- date last changed
- 2023-10-07 23:08:43
@article{f80d7ec8-2cfa-4bda-b2af-105bd75e04c5,
abstract = {{<p>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 (SiO<sub>2</sub>, (NO<sub>3</sub> <sup>–</sup> + NO<sub>2</sub> <sup>–</sup>)-N, Fe<sub>total</sub>, Mn<sub>total</sub>, pH, F<sup>−</sup>, Cl<sup>−</sup>, SO<sub>4</sub> <sup>2−</sup>, Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, and Mg<sup>2+</sup>) 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<sup>−</sup>, F<sup>−</sup>, Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>) was found due to dilution from mountain-side water release. Increase in (NO<sub>3</sub> <sup>–</sup> + NO<sub>2</sub> <sup>–</sup>)-N, SO<sub>4</sub> <sup>2−</sup>, and Mg<sup>2+</sup> concentration occurred locally due to soil leaching of contaminants or agricultural fertilizers through surface ruptures in recharge areas. Increase of SO<sub>4</sub> <sup>2−</sup> content also originated from leaching of marine clay in coastal areas and possibly sporadic deep crustal fluid upwelling. Increase in (NO<sub>3</sub> <sup>–</sup> + NO<sub>2</sub> <sup>–</sup>)-N and Cl<sup>−</sup> 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 Fe<sub>total</sub> and Mn<sub>total</sub> 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.</p>}},
author = {{Nakagawa, Kei and Yu, Zhi Qiang and Berndtsson, Ronny and Hosono, Takahiro}},
issn = {{0022-1694}},
keywords = {{Earthquake hydrology; Groundwater geochemistry; Kumamoto earthquake; Self-organizing maps}},
language = {{eng}},
publisher = {{Elsevier}},
series = {{Journal of Hydrology}},
title = {{Temporal characteristics of groundwater chemistry affected by the 2016 Kumamoto earthquake using self-organizing maps}},
url = {{http://dx.doi.org/10.1016/j.jhydrol.2019.124519}},
doi = {{10.1016/j.jhydrol.2019.124519}},
volume = {{582}},
year = {{2020}},
}