Strain Localization and Stress Evolution Along the Yangsan Fault: A Geodetic Approach to Seismic Hazard Assessment

This study addresses the lack of detailed geodetic assessments of crustal strain accumulation along the central Yangsan Fault in southeastern Korea, an area of recognized but insufficiently characterized seismic potential. To tackle this, we applied elastic strain tensor analysis to GNSS data from 33 stations, forming 49 triangular elements across the fault zone. From this, we quantified areal strain (Δ), maximum shear strain (γmax), and principal stress orientations (θp, θ_γmax) to map spatial deformation heterogeneity. The results identify several high-strain zones, notably Triangle 10 (2.984 µstrain/yr), Triangle 16 (2.325), and Triangle 31 (2.452), with Triangle 16—located at the Yangsan–Ulsan Fault intersection—exhibiting pronounced shear strain and a sharp angular deviation in stress orientation. These findings reveal localized stress reorganization likely caused by fault–fault interaction. Our analysis highlights the capability of GNSS-based strain tensor modeling to detect subtle intraplate deformation. The proposed methodology offers a practical framework for pinpointing structurally sensitive fault segments with elevated seismic risk in otherwise stable continental interiors, supporting more targeted seismic hazard assessment in Korea and other intraplate regions worldwide.