## 3 Results
### Strain Tensor Analysis and Spatial Characterization of Deformation
Table 2 summarizes the deformation parameter results derived from GNSS velocity data spanning from the first campaign in 2019 to the first campaign in 2020. For each of the 49 triangular elements, six key indicators were computed: the first and second principal strain rates (\(\varepsilon_{1}\), \(\varepsilon_{2}\)), principal axis orientation (\(\theta_{\text{p}}\)), maximum shear strain rate (\(\gamma_{\text{max}}\)), orientation of maximum shear (\(\theta\_{\text{-}\gamma_{\text{max}}}\)), and areal strain rate (\(\Delta\)). These parameters allow for quantitative interpretation of localized contraction/extension trends, shear concentration, and surface area changes. The average values for each parameter are listed at the bottom of the table. tectonic processes along the Yangsan Fault and its surrounding areas. The triangles with large strain values are as follows:  
* Triangle 6:
* Maximum Shear Strain: 1.513 \(\upmu\)strain/yr
* Shear Stress Direction: 54.81\({}^{\circ}\)
* Principal Strain: 2.498 \(\upmu\)strain/yr and 0.985 \(\upmu\)strain/yr
* Principal Axis Orientation: 99.81\({}^{\circ}\)
* Dilatation: 3.482 \(\upmu\)strain/yr  
This triangle exhibits very high principal strain and dilatation, suggesting a region of concentrated tectonic deformation. The elevated shear strain points to possible active faulting along or near the Yangsan Fault. The dilatation value indicates a region of significant extension, possibly reflecting a fault zone where strain is accumulating prior to potential fault rupture. * Triangle 10:
* Maximum Shear Strain: 2.984 \(\upmu\)strain/yr
* Shear Stress Direction: 23.30\({}^{\circ}\)
* Principal Strain: 2.367 \(\upmu\)strain/yr and \(-\)0.617 \(\upmu\)strain/yr
* Principal Axis Orientation: 68.30\({}^{\circ}\)
* Dilatation: 1.750 \(\upmu\)strain/yr  
Triangle 10 also demonstrates high shear strain, marking a region with intense deformation, likely linked to active fault movement along the Yangsan Fault system. The high dilatation value suggests localized extension in this zone, which could be an indicator of evolving tectonic dynamics and potentially significant deformation in the near future. * Triangle 11:
* Maximum Shear Strain: 1.105 \(\upmu\)strain/yr
* Shear Stress Direction: 27.30\({}^{\circ}\)
* Principal Strain: \(-\)2.241 \(\upmu\)strain/yr and \(-\)3.346 \(\upmu\)strain/yr
* Principal Axis Orientation: 72.30\({}^{\circ}\)
* Dilatation: \(-\)5.588 \(\upmu\)strain/yr  
This triangle shows negative strain values, indicating contraction or compression in the region. The large negative dilatation of \(-\)5.588 \(\upmu\)strain/yr suggests significant compressive stress in this area, which may reflect fault reactivation or stress accumulation. This could be an area where a potential earthquake may nucleate, particularly due to the contraction observed. * Triangle 45:
* Maximum Shear Strain: 1.442 \(\upmu\)strain/yr
* Shear Stress Direction: 80.89\({}^{\circ}\)
* Principal Strain: 1.906 \(\upmu\)strain/yr and 0.464 \(\upmu\)strain/yr
* Principal Axis Orientation: 125.89\({}^{\circ}\)
* Dilatation: 2.370 \(\upmu\)strain/yr  
Triangle 45 exhibits a balanced strain pattern, with both contraction and extension. The high dilatation value suggests that localized extension is occurring, which could be indicative of evolving fault dynamics. This area may be undergoing complex deformation, including both shear and tensional stress, and could represent a key area for monitoring as it might serve as a deformation zone between different fault segments. These high-strain values in specific triangles point to regions with notable deformation, likely indicative of ongoing tectonic processes or active faulting. Notably, Triangles 6 and 10, with their larger shear strain values, highlight areas with heightened seismic potential. These zones, with significant strain accumulation, are critical for future seismic hazard assessments and warrant detailed monitoring. The regions identified through this analysis are key to understanding the active tectonic processes in southeastern Korea.