[AHW24-P03] Change of groundwater radon concentration caused by 2016 Kumamoto earthquake
Keywords:The 2016 Kumamoto earthquake, Groundwater Radon concentration, Futagawa fault, Hinagu fault
Groundwater radon concentration changes have been reported as precursory indicators of earthquakes (e.g. Noguchi and Wakita, 1977; Kuo et al., 2006, 2011). Radium in rocks decays to produce radon and the radon is released from rock surface to pore. The rate of the radon release increase with the surface area, therefore the radon release can be indicative of the crustal deformation such as earthquake.
We report the results of groundwater radon concentration at 7, 11, 13, 18 and 19 months after the 2016 Kumomato earthquake. In Kumamoto area, fortunately groundwater radon had been measured in 2009, seven years before the Kumamoto earthquake (Tokunaga, 2010). We then discuss the change of groundwater radon concentration in relation to the fault rupture by comparing our data to Tokunaga (2010), i.e., before and after the quake.
The results of our measurement show that the groundwater radon indicate high concentration in the step and jog region of Futagawa and Hinagu faults both before and after the earthquake. The concentration around newly recognized surface fracture is significantly high. Although there is a difficulty in comparing the radon data directly with those from the previous work gained by different measurement device, the values of radon concentration in northern region from Futagawa and Hinagu fault are decreased after earthquake wheareas the values are increased in the southern region. In addition to appearing newly formed cracks in the northern region, our result suggests that the ground after the earthquakes is more permeable than before, causing decrease of 222Rn concentration in northern region, accordingly.