Abstract
Understanding near-trench interseismic deformation at subduction zones is crucial for assessing the hazards of giant earthquakes, especially trench-breaking tsunamigenic earthquakes, such as the 2011 Tohoku earthquake. However, interseismic locking preceding such trench-breaking tsunamigenic events remain poorly constrained due to the limited sensitivity of onshore geodetic observations. Here, we present seafloor geodetic observations along the southwestern Kuril trench, a region with the potential for large coseismic ruptures reaching the trench, as inferred from historical tsunami records. Our results show high slip-deficit rates near the trench during 2019–2024 and suggest that a slip deficit of 20.5–30.0 m may have accumulated over the past ~400 years, considering the long-term low seismic activity in this region. These findings imply future recurrence of a megathrust earthquake (Mw ~8.8) with rupture reaching the Kuril trench. Furthermore, they highlight the importance of seafloor geodetic monitoring for seismic and tsunami hazard assessment at subduction zones.
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Data availability
The numerical data for the displacement time series and displacement velocities presented in this study are provided in the Supplementary Information. The GNSS-A datasets that can be used for the positioning analysis and our positioning results are available from the data repository60: https://doi.org/10.5281/zenodo.18277176.
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Acknowledgements
We appreciate the Geospatial Information Authority of Japan and the Japan Meteorological Agency for distributing the F5 solutions of the GEONET and earthquake catalogs, respectively. Certain figures were generated using the Generic Mapping Tools software (version 6)59. This study was supported by the Japan Society for the Promotion of Science KAKENHI (Grant Number: 19H05596) and by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan under the Second and Third Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research). This study was also supported by the Cooperative Research Program of Atmosphere and Ocean Research Institute, the University of Tokyo (Research Vessel Shinsei-maru, Numbers: KS-19-12, KS-20-16, KS-21-05, KS-23-04, and KS-24-07).
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F.T. analyzed the GNSS-A datasets, calculated the observed and synthetic surface displacement rates for both onshore and offshore data, and wrote the manuscript. Y.O. organized the observation plan and directed observation activities. F.T., Y.O., M.K., M.O., H.T., R.H., and T.I. conducted the seafloor geodetic observations. All authors participated in the discussion of the results.
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Communications Earth and Environment thanks Sharadha Sathiakumar and the other anonymous reviewer(s) for their contribution to the peer review of this work. Primary handling editors: Sylvain Barbot and Joe Aslin. [A peer review file is available.]
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Tomita, F., Ohta, Y., Kido, M. et al. Seafloor geodetic evidence of slip deficit near the southwestern Kuril Trench. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03297-2
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DOI: https://doi.org/10.1038/s43247-026-03297-2
