Helium isotope anomaly in groundwater prior to the 2024 Noto Peninsula earthquake

Takanori Kagoshima (), Yuji Sano (), Naoto Takahata, Yume Kawamoto, Tomo Shibata, Ying Li, Tomoaki Morishita, Yoshihiro Hiramatsu and Junichi Nakajima
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Takanori Kagoshima: University of Toyama, Graduate School of Science and Engineering
Yuji Sano: Kochi University, Marine Core Research Institute
Naoto Takahata: University of Tokyo, Atmosphere and Ocean Research Institute
Yume Kawamoto: University of Toyama, Graduate School of Science and Engineering
Tomo Shibata: Fukuoka University, Department of Earth System Science
Ying Li: China Earthquake Administration, Institute of Earthquake Forecasting
Tomoaki Morishita: Kanazawa University, Faculty of Geosciences and Civil Engineering, Institute of Science and Engineering
Yoshihiro Hiramatsu: Kanazawa University, Faculty of Geosciences and Civil Engineering, Institute of Science and Engineering
Junichi Nakajima: Institute of Science Tokyo, Meguro, Department of Earth and Planetary Sciences

Nature Communications, 2025, vol. 16, issue 1, 1-9

Abstract: Abstract Intense earthquake swarms had been observed on the Noto Peninsula in north-central Japan since December 2020. We report data obtained by periodical groundwater sampling and helium isotope measurements in the epicentre area starting July 2022 for investigating the cause of this swarm. The data show mantle-derived helium reaching a maximum of 5 Ra where Ra is the atmospheric 3He/4He ratio of 1.39 × 10−6. This value indicates that the swarm was caused by fluids rising from the mantle. Time-series analysis show an anomalous drop in helium isotopic ratio prior to the 1 January 2024 Noto earthquake (M7.6), which seriously damaged the region. This decrease in helium isotopic ratio is possibly due to the degassing of radiogenic helium via the deformation of the rocks constituting the groundwater aquifer, which is fundamental and valuable data for predicting inland earthquakes in subduction zones. Periodical observation of helium isotopic ratios in deep groundwater is desirable in regions where a large earthquake is expected.

Date: 2025
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DOI: 10.1038/s41467-025-65717-9

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