Rheological Segmentation and Distributed Strain Partitioning in the Korean Peninsula Revealed by Fusion of InSAR–GNSS Velocity Fields

The Korean Peninsula provides a unique natural setting to investigate intraplate deformation driven by far-field Pacific and Philippine Sea plate forces. Despite its location along the nominally stable interior of the Eurasian Plate, the region hosts frequent seismicity and historical Mw ≥ 5.5 earthquakes, yet the spatial distribution and mechanisms of strain accumulation remain insufficiently constrained. Here we fuse multi-frame Sentinel-1 InSAR time series with dense GNSS observations (2017–2024) to produce a peninsula-scale, three-component surface deformation field. After rigorous frame corrections, GPS filtering, and removal of the Eurasia-fixed plate motion, the resulting velocity field reveals a sharp rheological and kinematic segmentation across the peninsula.

The fused horizontal field identifies a rigid western domain—the Gyeonggi Massif and western Okcheon Belt—with negligible residual motion, contrasted by a kinematically mobile southeastern domain (Yeongnam Massif and Gyeongsang Basin) showing coherent SW–WSW residual flow up to 3.5 mm/yr. Independent InSAR-derived vertical and E–W velocity components exhibit strong lateral gradients that correspond with mapped active faults and clusters of seismicity. Strain-tensor inversion indicates peninsula-wide ENE–WSW shortening, locally partitioned into dextral transpression along the Yangsan Fault System and distributed shear throughout the southeastern crust.

Integrating these geodetic observations with published crustal seismic-velocity models, we propose a rheology-driven strain-partitioning mechanism. The western peninsula is underlain by strong, felsic, low-Vp/Vs crust and acts as a continental backstop, whereas the southeastern block comprises weaker, mafic and magmatically modified crust that responds more readily to far-field compression. This lithospheric contrast explains the concentration of deformation, shear localization, and seismic strain accumulation within the southeastern block.

Our findings demonstrate that inherited crustal rheology—not block rotation alone—controls present-day intraplate deformation in Korea, offering a unified framework for understanding its seismicity distribution and improving seismic hazard assessment in slowly deforming continental interiors.