[A-HW30] Isotope Hydrology 2025

[AHW30-P01] Spatial Distribution of Lithospheric-Meteoric Water Mixing Ratio of Non-Volcanic Hot Springs Water around Median Tectonic Line, Southwestern, Japan

★Invited Papers

*Rofiqul Umam^1,2, Tsutomu Yamanaka^1,2, Ikuya Adachi³ (1.Faculty of Life and Environmental Sciences, University of Tsukuba, Japan, 2.Center for Research in Radiation, Isotopes, and Earth System Sciences (CRiES), University of Tsukuba, Japan, 3.Degree Programs in Life and Earth Sciences, University of Tsukuba, Japan)

Keywords:hot spring waters, isotope evolution model, lithospheric-meteoric water mixing ratio, non-vulcanic area, spatial distribution, median tectonic line

Natural hot springs in Non-volcanic southwestern Japan are generally believed to originate from slab-dehydrated fluid. However, the isotope composition of the fluid is usually altered by circulating meteoric water and/or seawater through upwelling flow to the surface. To investigate the original isotope composition distributed in the non-volcanic region of southwestern Japan, we conducted a spatial distribution of lithospheric-meteoric water mixing ratio using an isotope evolution model of lithospheric-enclosed waters. In addition, its geographic distribution is discussed within the framework of subduction zone tectonics along with the presence of fault and deep tremor zones. The results of the study show that the distribution of lithospheric-meteoric water mixing ratio along the Median Tectonic Line (MTL) has a fairly high average value. This result indicates that active faults influence the contribution of deep groundwater to a high percentage. In addition, the lithospheric-meteoric water mixing ratio distribution also reinforce the suspicion that active faults in southwestern Japan control the discharge of deep groundwater (lithospheric water) and have a positive correlation with tremor activity due to the production of slab-dehydrated fluids.