4:00 PM - 4:15 PM
[SCG59-03] Groundwater Gas Observation to Detect Interaction between Volcanic and Seismic Activities
Keywords:hot-spring water, continuous monitoring
In this presentation, we will present the results to date of continuous observations of dissolved gases in hot springs conducted in the Aso and Kumamoto regions.
The Kumamoto earthquake in 2016 caused significant damage, which started from an earthquake centered at the nodal point of the Hinagu and Futagawa faults. According to the resistivity structure of the area along the Futagawa Fault identified by Aizawa et al. (2021), a low resistivity zone C1 beside the focal point of the earthquake and a low resistivity zone C2 just below Mt Aso. If there is an interaction between the volcanic activity of Mt. Aso and the seismic activity of the Futagawa Fault, the fluid supplied from these low-velocity zones might play an important role. If so, there may be a correlation in the time series of the composition of deep source fluids supplied from C1 and C2. Therefore, our goal is to detect the deep-origin fluids supplied by C1 and C2.
According to Iwamori et al.(2023), hot springs with high helium isotope ratios are scattered in the Aso and Kumamoto areas. Observation equipment was installed at two of these hot springs, one along the Futagawa fault and the other in the Aso caldera, where dissolved gases were extracted and continuously observed with a quadrupole mass spectrometer. At the ASO station, the hot spring water that was constantly pumped from a sampling depth of 35 m was used for the observation. the composition began to be disturbed before the October 2021 eruption of Mt.Aso, and around January 2022, the disturbance disappeared, but the amount of atmospheric composition in the hot spring water increased significantly. This is the result of the relative decrease in the amount of deep-source gas supplied to the hot spring area before and after the eruption. On the other hand, at station KUM along the Futagawa Fault, hot spring water pumped intermittently from a sampling depth of 1100 m was used for observation. No change in the composition of the dissolved gas was observed during the eruption of Mt. Aso nor in response to the occurrence of earthquakes in the surrounding area.
The current results mean that the combination of ASO and KUM could not detect the interaction between earthquakes and volcanic activities. Therefore, we relocated the station along the fault to a new station OTN along the Futagawa fault, which is closer to Mt. Aso, and started observations in December 2022. The composition of dissolved gas here appears to be more stable than at KUM. We will continue to pay attention to changes in the data at OTN.
The Kumamoto earthquake in 2016 caused significant damage, which started from an earthquake centered at the nodal point of the Hinagu and Futagawa faults. According to the resistivity structure of the area along the Futagawa Fault identified by Aizawa et al. (2021), a low resistivity zone C1 beside the focal point of the earthquake and a low resistivity zone C2 just below Mt Aso. If there is an interaction between the volcanic activity of Mt. Aso and the seismic activity of the Futagawa Fault, the fluid supplied from these low-velocity zones might play an important role. If so, there may be a correlation in the time series of the composition of deep source fluids supplied from C1 and C2. Therefore, our goal is to detect the deep-origin fluids supplied by C1 and C2.
According to Iwamori et al.(2023), hot springs with high helium isotope ratios are scattered in the Aso and Kumamoto areas. Observation equipment was installed at two of these hot springs, one along the Futagawa fault and the other in the Aso caldera, where dissolved gases were extracted and continuously observed with a quadrupole mass spectrometer. At the ASO station, the hot spring water that was constantly pumped from a sampling depth of 35 m was used for the observation. the composition began to be disturbed before the October 2021 eruption of Mt.Aso, and around January 2022, the disturbance disappeared, but the amount of atmospheric composition in the hot spring water increased significantly. This is the result of the relative decrease in the amount of deep-source gas supplied to the hot spring area before and after the eruption. On the other hand, at station KUM along the Futagawa Fault, hot spring water pumped intermittently from a sampling depth of 1100 m was used for observation. No change in the composition of the dissolved gas was observed during the eruption of Mt. Aso nor in response to the occurrence of earthquakes in the surrounding area.
The current results mean that the combination of ASO and KUM could not detect the interaction between earthquakes and volcanic activities. Therefore, we relocated the station along the fault to a new station OTN along the Futagawa fault, which is closer to Mt. Aso, and started observations in December 2022. The composition of dissolved gas here appears to be more stable than at KUM. We will continue to pay attention to changes in the data at OTN.