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

[AHW24-P06] Tank model analysis of coseismic groundwater-level increasing induced by 2016 Kumamoto Earthquake

*Makoto Kagabu¹, Kiyoshi Ide², Takahiro Hosono², Kei Nakagawa¹, Jun Shimada³ (1.Faculty of Environmental Science, Nagasaki University, 2.Priority Organization for Innovation and Excellence, Kumamoto University, 3.Emeritus Professor, Kumamoto University)

Keywords:2016 Kumamoto earthquake, Groundwater level, Tank model analysis, Coseismic groundwater level rise

After the 2016 Kumamoto Earthquake, the amount of spring water in the Suizenji Park was greatly reduced and faced a depletion crisis, while groundwater level at the observation wells showing a drastic rise. In this study, this groundwater level rising was evaluated using a tank model to distinguish whether it was caused by the earthquake. This model were applied to regionally distributed groundwater observation wells to clarify the spatial distribution characteristics.

A tank model was constructed to explain groundwater level data recorded at the observation wells. The amount of daily precipitation subtracted from the evapotranspiration estimated by the Thornthwaite method in each month were used as effective input amounts to the first tank. Also, since paddy fields are expected to recharge groundwater during the paddy irrigation period from May to October, we added paddy tank. The water level in the third tank was regarded as the groundwater level, and the parameter value was adjusted in each observation well so as to explain the measured groundwater level.

By constructing a tank model that explain the long-term actual groundwater level (measured value) over the past two years until the Kumamoto earthquake occurs, the difference from the measured and calculated value was evaluated as the extent of coseismic groundwater level increase. The coseismic groundwater level rise was found to be particularly large on the east side of the epicenter.