Possibilities to perform pre- and post-seismic
groundwater chemical comparisons on re
gional
groundwater flow systems are rare due to lack of data and observations. The Kumamoto earthquake provides an unusual opportunity to improve the knowled
ge on earthquake hydrolo
gy 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 M
g2+) usin
g self-or
ganizin
g maps (SOM) combined with hydrolo
gical and
geolo
gical characteristics to improve the understandin
g of chan
ges in
groundwater chemistry after a major earthquake. The results indicate that the earthquake induced hydrolo
gical and environmental chan
ge via fault formin
g (Suizenji fault systems), liquefaction, rock fracturin
g, and
ground shakin
g. These
geolo
gical processes created rock fresh reactive surfaces, rock loosenin
g, 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 hydrolo
gical and environmental chan
ge was from the increased dissolved silica content stemmin
g from fracturin
g and Si-O bond cleava
ge in silicate rocks. Besides this, decreasin
g 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 M
g2+ concentration occurred locally due to soil leachin
g of contaminants or a
gricultural fertilizers throu
gh surface ruptures in rechar
ge areas. Increase of SO4 2− content also ori
ginated from leachin
g of marine clay in coastal areas and possibly sporadic deep crustal fluid upwellin
g. Increase in (NO3– + NO2– )-N and Cl− content occurred from sewa
ge water pipe breaks in the Suizenji fault formation in urban areas. Decrease of pH occurred in a few wells due to mixin
g of river water and different types of aquifer
groundwater. Increase of Fetotal and Mntotal concentration possibly ori
ginated from leachin
g of marine clay by liquefaction in coastal areas. However, in most cases the water chemistry chan
ges
gb(0,0,0); FONT-SIZE: 7.173pt; mso-spacerun: 'yes'">were subtle, thus not resulting in any groundwater quality deterioration of water supp