[A-HW19] Tracer Hydrology: Advances in Measurement and Modelling

[AHW19-04] A preliminary look into the spatiotemporal variability of gas composition and isotopes along the Fujikawa-Kako Fault Zone

*Ma Teresa Nakajima¹, Naoto Takahata², Yuji Sano¹, Stephanie Musy³, Yama Tomonaga^3,4, Oliver S. Schilling^3,5 (1.Marine Core Research Insitute, Kochi University, Monobe Campus, Kochi, Japan, 2.Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa Campus, Chiba, Japan, 3.Hydrogeology, Department of Environmental Sciences, University of Basel, Switzerland , 4.Entracers GmbH, Dübendorf, Switzerland, 5.Department Water Resources and Drinking Water, Eawag–Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland)

Keywords:Noble Gas Isotopes, Helium , Gas Composition, Mt. Fuji

Mt Fuji’s last known eruption was in 1707, a few months after the Nankai Megathrust Earthquake. As the Nankai Trough is overdue for another earthquake and with the recent earthquakes in adjacent areas such as the New Year’s deadly tremor in the Noto Peninsula, it is worth monitoring possible earthquakes and magma fluid activities under Mt Fuji. Volcanic fluids and gases travel faster along preferential gas pathways. The Fujikawa-Kako fault zone is a suitable candidate for observing the changes in gas composition and isotopes associated with earthquakes and magmatic fluids. We collected water samples at several sampling points in the Fujinomiya area. Preliminary results show that the N2 is the dominant gas in all the sites with low O2 and high CO2 concentrations typical of groundwater with volcanic influence. Helium isotope ratio was higher in areas where water is pumped from deeper sources. This study shows the baseline values for these gases in the area and it is crucial that we continue the observation for possible imminent changes in the volcanic system.