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

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 R_a where R_a 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

SUBMITTER: Kagoshima T 

PROVIDER: S-EPMC12657891 | biostudies-literature | 2025 Nov

REPOSITORIES: biostudies-literature