5:15 PM - 6:45 PM
[U15-P58] Geochemical observation research of material cycles beneath the northeastern Noto Peninsula from 2022
Keywords:The Noto earthquake swarm, The 2024 Noto Peninsula Earthquake, Geochemical cycles, Noble gas isotopes
The earthquake swarm at the northeastern Noto Peninsula, including the 2024 Noto Earthquake, has continued for a long duration. The behavior of a highly pressurized deep fluid seems to be a possible driving force of this earthquake swarm activity (Amezawa et al., 2023; Yoshida et al., 2023; Nishimura et al., 2023). In this area, Umeda et al. (2009) reported hot spring data with 3He/4He ratios higher than the atmosphere, indicating high contributions of the mantle-derived component. Earthquakes can change underground situations such as structures of groundwater system, which results in changes of groundwater chemistry (e.g., Tsunogai and Wakita, 1995). Also in the northeastern Noto Peninsula, it is expected that variations of chemical and isotopic compositions of springs reflect deep-shallow underground situations during the earthquake swarm period.
In order to elucidate geochemical cycles beneath the northeastern Noto Peninsula during the earthquake swarm period, temporal variations of spring chemical and isotopic compositions were investigated in this study. Spring water and gas samples at eight sites were collected continuously from June 2022 to February 2024. In University of Toyama, anion (Cl-, SO42-) concentrations in the water samples were measured using an ion chromatography 883 basic IC plus, and δ18O and δD values of water were determined using an isotope analyzer L2130-i. For the water samples collected in copper tubes and glass containers, dissolved gas components were extracted into gaseous phases by a head space method. In Atmosphere and Ocean Research Institute, the obtained gas samples were introduced into a vacuum line for purification. Subsequently 4He/20Ne ratios were measured using a quadrupole mass spectrometer, and 3He/4He ratios were analyzed using a noble gas mass spectrometer Helix-SFT. The obtained noble gas data were calibrated against ASW (air-saturated water) and air data.
Remarkable changes of chemical data were observed at the site ASY located in the cluster S area which is thought to be on the deep fluid supply source (Amezawa et al., 2023). Between May and October 2023, anion concentrations, δ18O values and δD values were lower than those in 2022. However, from October 2023 to January 2024, just after the M7.6 earthquake, the concentrations and isotopic ratios increased to values close to those observed in 2022. An average of the air-corrected 3He/4He ratios of the samples collected in 2022 was 2.94+/-0.07 Ra (1σ) (1Ra: the atmospheric 3He/4He ratio of 1.4×10-6). The air-corrected 3He/4He ratio decreased to 2.3 Ra in July 2023, and increased to 3.2 Ra in January 2024, just after the M7.6 earthquake. Temporal variations of anion concentrations, δ18O values and δD values may be related to changes of permeability of aquifer rocks. Temporal variations of 3He/4He ratios may reflect changes of contributions from the deep fluid with mantle-derived components due to the behavior of the deep fluid, or water-rock reactions associated with increase of cracks due to seismic activity. In the presentation, data obtained at other sampling sites will be also compared and geochemical cycles beneath the northeastern Noto Peninsula from 2022 will be further discussed.
(References)
Amezawa et al. (2023) GRL 50, e2022GL102670.; Nishimura et al. (2023) Sci. Rep. 13, 8381.; Tsunogai and Wakita (1995) Science 269, 61-63.; Umeda et al. (2009) JGR solid Earth 114, B01202.; Yoshida et al. (2023) JGR solid Earth 128, e2022JB026047.
In order to elucidate geochemical cycles beneath the northeastern Noto Peninsula during the earthquake swarm period, temporal variations of spring chemical and isotopic compositions were investigated in this study. Spring water and gas samples at eight sites were collected continuously from June 2022 to February 2024. In University of Toyama, anion (Cl-, SO42-) concentrations in the water samples were measured using an ion chromatography 883 basic IC plus, and δ18O and δD values of water were determined using an isotope analyzer L2130-i. For the water samples collected in copper tubes and glass containers, dissolved gas components were extracted into gaseous phases by a head space method. In Atmosphere and Ocean Research Institute, the obtained gas samples were introduced into a vacuum line for purification. Subsequently 4He/20Ne ratios were measured using a quadrupole mass spectrometer, and 3He/4He ratios were analyzed using a noble gas mass spectrometer Helix-SFT. The obtained noble gas data were calibrated against ASW (air-saturated water) and air data.
Remarkable changes of chemical data were observed at the site ASY located in the cluster S area which is thought to be on the deep fluid supply source (Amezawa et al., 2023). Between May and October 2023, anion concentrations, δ18O values and δD values were lower than those in 2022. However, from October 2023 to January 2024, just after the M7.6 earthquake, the concentrations and isotopic ratios increased to values close to those observed in 2022. An average of the air-corrected 3He/4He ratios of the samples collected in 2022 was 2.94+/-0.07 Ra (1σ) (1Ra: the atmospheric 3He/4He ratio of 1.4×10-6). The air-corrected 3He/4He ratio decreased to 2.3 Ra in July 2023, and increased to 3.2 Ra in January 2024, just after the M7.6 earthquake. Temporal variations of anion concentrations, δ18O values and δD values may be related to changes of permeability of aquifer rocks. Temporal variations of 3He/4He ratios may reflect changes of contributions from the deep fluid with mantle-derived components due to the behavior of the deep fluid, or water-rock reactions associated with increase of cracks due to seismic activity. In the presentation, data obtained at other sampling sites will be also compared and geochemical cycles beneath the northeastern Noto Peninsula from 2022 will be further discussed.
(References)
Amezawa et al. (2023) GRL 50, e2022GL102670.; Nishimura et al. (2023) Sci. Rep. 13, 8381.; Tsunogai and Wakita (1995) Science 269, 61-63.; Umeda et al. (2009) JGR solid Earth 114, B01202.; Yoshida et al. (2023) JGR solid Earth 128, e2022JB026047.