[S-CG54] New Insights of Fluid-Rock Interactions: From Surface to Deep Subduction Zone

[SCG54-06] Geofluid Origins in the Noto Peninsula: Li and Sr Isotopic Insights Before and After the 2024 M7.6 Earthquake

*Zahra Zandvakili^1,2, Takanori Kagoshima³, Tomoaki Morishita⁴, Yoshihiro Hiramatsu⁴, Manato Akishiba¹, Yoshiro Nishio¹ (1.Kochi university , 2.Fukushima university , 3.University of Toyama, 4.Kanazawa university )

Keywords:Noto Peninsula 2024 Earthquake , Isotope, Geochemistry , Precursor

The earthquake swarm began in late November 2020 in the northeatern tip of the Noto Peninsula. The occurrence of swarms in the Noto Peninsula (which include four clusters: northern, northeastern, western, and southern—the latter being the first to begin; Amezawa et al., 2023) has been linked to the migration of fluids (e.g., Nakajima, 2022; Yoshida et al., 2023a; Nishimura et al., 2023). This is further supported by the presence of low seismic velocity and low resistivity zones beneath the earthquake swarm area, suggesting the existence of fluids in the lower crust and/or upper mantle (Yoshimura & Nakajima, 2022; Yoshida et al., 2023b; Yoshimura et al., 2024). The M7.6 Noto Peninsula earthquake in 2024 is thought to be linked to this swarm, as Peng et al. (2024) described a complex evolution process connecting swarm activity to the nucleation of the M7.6 mainshock. In order to clarify the origin of geofluids involved in this seismic activity, we analyzed Li and Sr isotope ratios of hot spring and groundwater samples collected from 11 sites on the Noto Peninsula between 2022 and 2024. Our findings reveal distinct variations in the isotope signatures, with Li and Sr isotope ratios, as well as elemental ratios such as Cl/Li, showing diverse characteristics. While the Li and Sr isotopes at several sites suggest the possibility of contributions from deep-seated fluids, the elevated Cl/Li ratios observed indicate significant mixing with shallow groundwater and ancient seawater. Furthermore, time-series analyses of Li isotope from two sites demonstrate changes prior to the M6.5 earthquake in May 2023.