Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW24] Hydrological change after the 2016 Kumamoto earthquake

Tue. May 22, 2018 3:30 PM - 5:00 PM A02 (Tokyo Bay Makuhari Hall)

convener:Jun Shimada(Graduate school of Science and Technology, Kumamoto University), Kei Nakagawa(Graduate School of Fisheries Science and Environmental Studies, Nagasaki University), Takahiro Hosono(熊本大学大学院先導機構, 共同), Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Chairperson:Shimada Jun(熊本大学先導機構), Hayashi Takeshi(Faculty of Education and Human Studies, Akita University)

4:05 PM - 4:20 PM

[AHW24-09] Coseismic groundwater quality change after the Kumamoto earthquake using long-term public observation data

*Masaki Yukako1, Takahiro Hosono2, Shimada Jun2 (1.Graduate School of Science and Technology, Kumamoto University, 2.Priority Organization for Innovation and Excellence, Kumamoto Universtity)

Keywords:groundwater, Kumamoto earthquake , water quality change

A severe earthquake occurred in Kumamoto district, Japan in April, 2016. Many investigators have been reported coseismic groundwater quality change over the world; however, most of these studies were focused only on point monitoring sites and water quality change in the context of regional groundwater flow dynamics has not been understood well due to the lack of numbers of monitoring wells and monitoring record to compare before and after the quake. However, in Kumamoto area, where hydrogeological conditions are well studied with plenty number of monitoring wells, there are long-term public observation data which provide us an excellent opportunity to investigate coseismic hydrochemical changes in detailed scale.
I analyzed change of groundwater hydrochemistry before and after the Kumamoto earthquake using above mentioned monitoring data for the past 10 years at 135 wells. Results show that hydrochemistry changes were confirmed in 34 items among 96 examined chemistry, including the increase of soluble silicon and decrease of evaporation residue and chlorine after the earthquake. Changing manner differs depending on each water quality item and areas. It is suggested that the most soluble silicon contained in the crust was increasingly dissolved in water due to rock deformation in the time of seismic fracture formation. The decrease of evaporation residue was remarkable near the Suizenji fault where the water level declined was confirmed recently. It is suggested that water of low concentration has flowed along this fracture systems and dilute deep groundwater. In coastal areas, chlorine concentrations were drastically reduced due to vertical water mixing effect driven by theliquefaction.
This study is important from the view point of groundwater conservation.