Seeing Japan's Crust in Finer Detail with Ultra-Dense GNSS Networks

Monitoring Earth’s surface deformation is fundamental to many areas of geoscience. To support such monitoring, GNSS networks have been deployed worldwide at national and regional scales. In Japan, the Geospatial Information Authority of Japan operates the GNSS Earth Observation Network System (GEONET), a continuous nationwide array that has underpinned a wide range of Earth-science advances. However, the typical spacing of GEONET stations can limit our ability to resolve deformation signals with short spatial wavelengths.

Over the last decade, Japanese mobile network operators have also constructed their own GNSS reference-site networks, primarily to improve positioning services. Ohta and Ohzono (Earth, Planets and Space, 2022) evaluated the SoftBank Corp. network from the perspective of crustal deformation monitoring. With more than 3,300 sites, about 2.5 times as many as GEONET, the network offers an exceptionally dense sampling of the Japanese islands. Their study showed that, with appropriate quality control, private-sector GNSS data can provide robust information for geodetic applications.

Building on these efforts, the Graduate School of Science at Tohoku University, together with SoftBank Corp. and ALES Corporation, launched an academic–industry consortium, “the Consortium to Utilize the SoftBank Original Reference Sites for Earth and Space Science”, to facilitate geoscientific use of SoftBank GNSS observations. Results obtained through this framework demonstrate the value of ultra-dense GNSS coverage for capturing diverse deformation processes, including aseismic deformation in the Noto Peninsula (Nishimura et al., Sci. Rep., 2023), coseismic slip associated with the 2024 Noto Peninsula earthquake (Yamada et al., EPS, 2025), and afterslip off western Sado Island (Ohtate et al., EPS, 2025). The same dense coverage is also enabling unusually detailed characterization of interseismic strain accumulation across Japan (Ohtate et al., in revision). In addition, a comprehensive assessment of the accuracy of the underlying coordinate time series has been conducted, demonstrating that the quality of the daily coordinates from GEONET and the SoftBank network is nearly equivalent (Ohta and Ohtate, EPS, 2026).

In this presentation, we summarize these recent outcomes and discuss how ultra-dense GNSS networks can expand the scope and resolution of crustal deformation research.

Acknowledgments: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science".