[M-IS09] Interdisciplinary studies on pre-earthquake processes

[MIS09-P08] The Fluctuations of the Soil Radon Fluxes near the Ground Surface at Two Different Depths at the Asahi Station Japan

Shiori Fukunaga¹, *Chie Yoshino², Katsumi Hattori^2,3,4, Toshiharu Konishi⁵ (1.Graduate School of Science and Engineering, Chiba University, 2.Graduate School of Science, Chiba University, 3.Center for Environmental Remote Sensing, Chiba University, 4.Research Institute of Disaster Medicine, Chiba University, 5.OHYO KOKEN KOGYO Co., Ltd.)

Keywords:Multi-channel singular spectrum analysis, soil radon concentration, soil radon flux, precipitation

Short-term earthquake forecast is important for mitigating the damage caused by major earthquakes such as the 2011 Tohoku earthquake and the 2024 Noto Peninsula earthquake, but it has not yet been achieved. There have been reports that the radon concentration in the atmosphere and the radon concentration in groundwater showed abnormal levels prior to the 1995 Hyogo-ken Nanbu earthquake, and the relationship between changes in radon concentration and major earthquakes has attracted attention. However, there are problems with the time resolution and sensitivity of the measuring equipment, and it has not yet been possible to show a statistically significant correlation with earthquakes. Therefore, we have developed a radon observation device that can measure the soil radon concentration in the ground near the surface with high sensitivity, and we are using this device in this study. This device is a radon monitor made by OHYO KOKEN KOGYO Co., Ltd. and is a device that detects alpha rays. In a previous study, the soil radon concentration in the ground was measured using a radon monitor, and the atmospheric tides were removed from the data by using atmospheric pressure and temperature data and MSSA (multichannel spectral singular value analysis) to estimate the soil radon flux in the ground near the surface. However, it was also found that in the case of heavy rain (more than 20 mm of precipitation per hour), the effect of precipitation was indicated. In order to realize earthquake forecast using radon observation, it is necessary to remove these fluctuations. Therefore, in this study, radon monitors were installed at different depths of 60 cm and 100 cm, and the soil radon flux was estimated using MSSA, as in previous studies, to examine the differences in flux intensity according to depth and the differences in the effects of precipitation due to heavy rain.