[O-06] Poster presentations by senior high school students

[O06-P33] Earthquake Prediction by Evaluating Water Quality

*Mizuki Tanaka¹, *Nayu Asada¹, *Chihiro Ikeda¹ (1. Fukui Prefectural Fujishima High School)

Keywords:concentration of chloride ions, predict earthquakes, a Type III blank area

we focused on groundwater quality in order to predict when and where earthquakes will occur and their magnitude. Our study has two objectives: first, to clarify the correlation between ground water quality and occurrence of earthquakes, and second, to explore the possibilities and challenges of analyzing ground water quality in earthquake prediction. We hypothesized that we could predict earthquakes by using the concentration of chloride ions in groundwater that gushes out in areas where active faults exist as an indicator of changes in stress (resistance force that occurs inside an object when an external force is applied to it). For the experiment and verification, we decided to use the Kawai area, which was the epicenter of the earthquake that occurred on September 4, 2020, as our water sampling site. We sampled water once a week, and recorded the date, time, and water temperature. We analyzed the collected water for chloride ion concentrations using an ion chromatograph analysis equipment at the Fukui Prefectural Institute of Education to determine its relationship to the actual earthquake that was felt in Fukui Prefecture. The results of the experiment showed that chloride ion concentrations tended to rise before the earthquakes and fall after it occurs. We made two observations on this result: First, we examined changes in water temperature. The correlation coefficient between changes in chloride ion concentration, which correlates with earthquakes in Fukui Prefecture, and changes in groundwater temperature is weakly negative at about -0.5, so we concluded that there is a correlation between earthquakes and groundwater temperature. However, subsoil water of the Kuzuryu River flows above the groundwater, and this subsoil water is easily affected by the outside air, so the temperature of the subsoil water tends to be high in summer and low in winter. Groundwater temperature also tends to be higher in summer and lower in winter, which is similar to the change in temperature of subterranean water, suggesting that groundwater temperature is affected by subterranean water when it is collected. Second, the mechanism by which ion concentrations change is discussed. First, the groundwater in the Kawai area sampled in this study shows stress-related changes in the amount of groundwater flowing out of the fault zone due to hot springs located nearby and seismic activity. Although the concentration of contained substances and other parameters are basically constant in subterranean groundwater, in the groundwater of this study, the mixing ratio of deep groundwater containing chloride ions seeping from the fault fracture zone originating from the ocean floor changed due to changes in stress. Through this study, it was found that before the earthquake, the proportion of deep water in the groundwater increased due to increased stress on the active fault, and after the earthquake, the amount of deep water squeezed out tended to decrease due to the release of stress. In other words, before the earthquake, the chloride ion concentration gradually increases with increasing stress, and immediately after the earthquake, the chloride ion concentration tends to reach its peak and then decrease.