Research conducted by Professor Tsutomu Yamanaka of the University of Tsukuba’s Institute of Life and Environmental Sciences and the Center for Research in Isotope and Environmental Dynamics (CRiES) has been featured in the January 2026 issue of Nikkei Science under the special topic “Approaching Deep Fluids.”

The feature explores the relationship between deep fluids circulating beneath the Japanese archipelago and seismic and volcanic activity. Deep fluids refer to water originating from the Earth’s mantle or subducting oceanic plates. Their behavior can be traced through the chemical compositions of hot spring waters and volcanic rocks—essentially serving as geological “letters from underground.”

The article introduces key findings from Professor Yamanaka and colleagues, who analyzed long-term changes in deep fluid activity in the Arima hot spring region. Through stable isotope analysis of hydrogen and oxygen in hot spring waters, the research team revealed that the supply of deep fluids temporarily increased before and after the 1995 Great Hanshin–Awaji Earthquake. Estimates suggest that 260,000–420,000 cubic meters of deep fluid may have surged upward from the crust during that period.

These findings provide an important clue that deep fluid dynamics may influence seismic activity, offering a new perspective for understanding earthquake generation mechanisms. The research also indicates that central Japan may represent one of the world’s rare examples of a “subsurface heavy-rainfall zone.”

The feature highlights two international papers that form the core of this research (Adachi & Yamanaka, 2024; Yamanaka & Adachi, 2024), both of which recently received the Japan Society of Hydrology and Water Resources Excellent Article Award. The studies, focusing on ultra-deep hydrological circulation, have garnered significant recognition both in Japan and internationally.

This research represents a major step toward understanding the link between deep water circulation and crustal processes and opens new pathways for disaster science and earthquake forecasting.

Full details can be found in the January 2026 issue of Nikkei Science.
We encourage you to take a look.

Related Publications

• Adachi, I., & Yamanaka, T. (2024). Isotopic evolutionary track of water due to interaction with rocks and its use for tracing water cycle through the lithosphere. Journal of Hydrology, 628, 130589. DOI:10.1016/j.jhydrol.2023.130589
• Yamanaka, T., & Adachi, I. (2024). Hot springs reflect the flooding of slab-derived water as a trigger of earthquakes. Communications Earth & Environment, 5, 459. DOI:10.1038/s43247-024-01606-1

Research Contact

Tsutomu Yamanaka
Institute of Life and Environmental Sciences / CRiES
University of Tsukuba
Field of Expertise: Hydrology, Physical Geography