[S-GC32] Volatiles in the Earth - from Surface to Deep Mantle

[SGC32-03] Geochemical characteristics of groundwater before 2018 Hokkaido Eastern Iburi earthquake

★Invited Papers

*Zahra Zandvakili¹, Yoshiro Nishio¹, Yuji Sano¹ (1.Kochi University )

Keywords:Hokkaido estern Iburi earthquake, Lithium isotope, Geochemistry , Earthquake precursor

Observation of groundwater geochemistry plays a crucial role in identifing the origin of fluids and may reveal traces of the mixing of fluids from different sources before a large earthquake. However, it is difficult to routinely observe groundwater geochemistry prior to a large earthquake. Using commercially available bottled drinking water, Tsunogai and Wakita (1995) revealed an increase in chloride ion concentrations in groundwater before the M7.2 1995 Kobe earthquake. Employing a similar approach, Sano and his group have focused on the isotopic composition of volatile elements such as hydrogen, oxygen, and carbon in groundwater prior to several major earthquakes (Sano et al., 2020a, Sano et al., 2020b,Onda et al., 2018). Sano et al. (2020a) specifically emphasized that changess in carbon isotope ratios, noted a few months before the M6.7 earthquake in eastern Hokkaido, Japan, in 2018, were attributed to the migration of carbon dioxide into the groundwater. To investigate potential signatures of deep fluid within the CO₂-fluid that entered the groundwater before the 2018 Hokkaido Eastern Iburi earthquake, we analyzed the temporal variations in isotopic ratios of nonvolatile elements such as Li and Sr. These elements serve as key indicators of the source of fluid within the groundwater. The results of this study indicate that the CO2 injected into the groundwater near the epicenter before the earthquake, as revealed by Sano et al. (2020a), was not accompanied by water originating from deep underground.