## 5 Results
### Calculation of the Geodetically Based Parameters
#### 5.1.4 Area Strain (AS)  
The Area Strain (AS) parameter is characterized by two different types: (i) dilatation, associated with extensional tectonics, and ii) compaction, related to compressional tectonics. The AS results indicate a clear dilatation dominance over compaction (Figure 7a), with values ranging between \(-596\times 10^{-9}\) (compaction) and \(2715\times 10^{-9}\) (dilatation), suggesting an almost 4.5 times higher dilatation than compaction (Figure 7b,c).  
Figure 6: Maximum Shear Strain (MaxSS) in the broader Strymon area: (**a**) MaxSS values (red circles) of the total examination points; (**b**) MaxSS values grid, based on the interpolation (kriging) geostatistical analysis.  
Although the dilatation type prevails within the study area (Figure 7b), it unevenly coexists in several cases with compaction, implying the involvement of shear. In particular, the maximum values' concentrations are documented strictly within the Strymon basin region, along the eastern boundary, as well as south of Kerkini Lake (northwestern part of the Strymon basin boundary). Moreover, it is worth mentioning the significant dilatation values observed at the central and eastern part of Mt Belles at the northwestern part of the study area. Regarding the high-value compaction concentrations (Figure 7c), they are mainly observed along the eastern margin of Strymon basin, southwesterly of the western Strymon basin margin within the broader Mt Vertiskos area, near the coastal  
Figure 7: Area Strain (AS) in the broader Strymon area: (**a**) calculated dilatation (blue circles) and compaction (red circles) values; (**b**) dilatation values grid, based on the interpolation (kriging) geostatistical methodology; (**c**) compaction values grid, based on the interpolation (kriging) geostatistical methodology.  
part of the Orfanos Gulf region and in the north part of the Drama basin (close to Kato Nevrokopi village).  
A significant difference between dilatation and compaction values indicates extensional (dilatation > compaction) or compressional (compaction > dilatation) active tectonics occurrences, while similar dilatation and compaction values show shear tectonics activity [57]. For instance, in the broader Kerkini Lake and Mt Belles area, the compaction values are absent or extremely low, indicating that this part of the study area is dominated by extensional active tectonics, manifested by dip-slip, normal faults (or fault zones). Regarding the sensu stricto area of Strymon basin, a clear dilatation (qualitative and quantitative) prevalence over compaction is documented; however, the compaction occurrence is noteworthy, showing that, despite the dilatation dominance, a significant shear component is observed, leading to active oblique-slip, normal faults (or fault zones') occurrence. Finally, the similar dilatation and compaction values at the southern part of the study area (Amphipolis-Paleokomi-Galiposos-Ofrynion area), where the Strymon River discharges into the North Aegean Sea, indicates potentially active strike-slip tectonic structures, extending within the offshore North Aegean region, which are associated with the tectonically and seismologically active strike-slip North Aegean Trough (NAT) fault zones.