Coseismic Surface Deformation and Fault Slip Distribution of the 2026 Mw 6.8 Kumamoto Earthquake from Multi-Sensor InSAR and GNSS Observations

On 28 July 2026, an Mw 6.8 earthquake occurred in Kumamoto, central Kyushu, Japan, near the Futagawa-Hinagu fault system.We used three Sentinel-1 C-band interferograms, two Advanced Land Observing Satellite-2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) interferograms, and one ALOS-4 PALSAR-3 L-band interferogram, along with Global Navigation Satellite System (GNSS) observations, to characterize coseismic deformation and fault slip.The interferometric synthetic aperture radar (InSAR)-derived line-of-sight (LOS) displacements agreed with GNSS-measured coseismic displacements projected into the corresponding LOS directions, with a root mean square error (RMSE) of 0.042 m and a correlation coefficient of 0.91.Sentinel-1 coherence decreased near the epicentral fault zone, whereas the ALOS-2/4 L-band interferometric data preserved greater coherence and resolved larger near-field displacement gradients.Joint inversion of the six InSAR LOS displacement fields and three-component GNSS displacements reproduced the observations with an overall RMSE of 0.056 m.The preferred model is primarily right-lateral, with net slip reaching approximately 2.98 m near 5 km depth and a weaker normal component at shallow depth.Two principal slip concentrations occurred near the epicenter and southwestward.The inferred seismic moment (1.85 × 10 19 N m), Mw 6.78, and the rake (approximately -175°) were consistent with independent seismological estimates.These results provide early geodetic constraints on the 2026 Kumamoto earthquake and demonstrate the value of integrating multi-frequency InSAR with GNSS for rapid source characterization.