Seismic Observation and Network Development
■ In April 1973, I initiated seismicity studies in the southern Hidaka Mountains and surrounding regions using optical film records from the Urakawa Seismological Observatory (KMU) of Hokkaido University, together with pen-recorder records from the Sapporo (SAP), Erimo (ERI), and Hiroo (MYR) observatories. Additional waveform data from the Japan Meteorological Agency (JMA) high-sensitivity volcano observatories and the Tohoku University Kitakami seismic network were incorporated to improve hypocenter determination accuracy.
■ Beginning in 1976, I contributed to the construction of a nine-station wireless telemetry seismic network (six stations in the Hidaka region and three stations at Sapporo–Misumai, Esan, and Akkeshi). Using digitally transmitted waveform data centralized at Hokkaido University, we conducted systematic investigations of microearthquake activity (M < 3) across Hokkaido and adjacent regions and developed associated analysis software.
■ Subsequently, I was involved in the introduction of satellite telemetry systems, real-time data exchange with the Sapporo District Meteorological Observatory, and implementation of the WIN waveform processing system developed by the Earthquake Research Institute, University of Tokyo. These developments contributed to the modernization and integration of nationwide real-time seismic waveform data sharing among universities, JMA, and NIED, enabling broad Internet-based access to seismic data across Japan.

Temporary Observations, Ocean-Bottom Seismology, and International Collaborations
■ I participated in urgent aftershock observation campaigns following major destructive earthquakes, including the 1973 Nemuro-oki, 1982 Urakawa-oki, 1993 Hokkaido Nansei-oki, 1995 Hyogo-ken Nanbu (Kobe), and 2003 Tokachi-oki earthquakes.
■ Using pop-up ocean-bottom seismometers (OBS), we conducted seismicity and crustal structure investigations in several offshore regions, including the junction of the Kuril and Japan Trenches. In particular, temporary OBS deployments within the source area of the 1952 Tokachi-oki earthquake (M8.2) allowed us to detect microearthquake clusters shortly before the 2003 Tokachi-oki earthquake.
■ As part of international collaborations, I contributed to the construction of the world’s first long-term unmanned telemetry seismic observation system at Mount Erebus (3,794 m), Ross Island, Antarctica. The system demonstrated multi-year continuous seismic monitoring capability under extreme polar winter conditions (−50 to −60°C). Additional international projects included seismic network development in West Java, Indonesia (JICA-supported technical cooperation), and marine crustal structure surveys offshore Norway, Iceland, and in the Caribbean region.

Seismic Wave Analysis and Numerical Modeling
■ In collaboration with the Institute of Statistical Mathematics, I developed an automatic real-time seismic phase detection method based on state-space modeling and the Akaike Information Criterion (AIC). This method enabled objective and high-precision automatic determination of P- and S-wave arrival times and significantly improved hypocenter location capability. The work received international recognition, and I was invited to present at the European Geophysical Union International School on Earthquake Prediction and Engineering (Plovdiv, Bulgaria).
■ Using supercomputers at Hokkaido University, I conducted numerical experiments based on the Cagniard–de Hoop exact ray theory to analyze seismic wave reflection and refraction processes and to re-evaluate crustal structures derived from marine seismic surveys.
■ By applying state-space modeling to broadband seismic records, I successfully extracted intrinsic attenuation (Low-Q) structures beneath volcanic front regions and demonstrated consistency with independently derived seismic tomography results.

Crustal Deformation and Strain Observation
■ I participated in high-sensitivity crustal strain observations using Sacks–Evertson borehole volumetric strainmeters developed at the Carnegie Institution of Washington and installed at the Urakawa Observatory.
■ Applying state-space modeling to strain data recorded before and after the 2003 Tokachi-oki earthquake (Mw 8.0), we identified a postseismic slow-slip event characterized by a two-stage slip model: four days of contraction followed by twenty-three days of expansion. The event was interpreted as quasi-static reverse slip occurring along the upper plane of the Wadati–Benioff zone, nearly coincident with the mainshock rupture area.

Major Contributions to Earth Sciences
■ First 3D imaging of P-wave velocity anomalies beneath the Hidaka Mountains down to approximately 100 km depth
■ Demonstration of an east–west compressional stress field beneath southern Hokkaido, supporting the westward motion hypothesis of the Kuril forearc sliver
■ Detection of precursory changes in seismicity patterns prior to major earthquakes
■ Identification of microearthquake clusters in offshore source regions through OBS observations
■ Demonstration of spatial correspondence between Low-Velocity and Low-Q zones beneath volcanic front regions
■ Development of objective real-time seismic phase detection methods based on state-space modeling