## 6 Discussion  
The combination of different techniques and methods is crucial for better assessing the tectonic regime of a region, as different aspects are enlightened. Initially, the GNSS data analysis indicates a low strain pattern for the broader Strymon region, except for a few locations, mostly lying at the eastern boundary of the Strymon basin. These data compare well with existing geological data derived from palaeoseismic trenching, which similarly highlight the most significant tectonic activity at the eastern part of the study area. Regarding the InSAR analysis, no horizontal rates (e.g., below resolution) have been traced in the E-W direction, whereas limited vertical motions have been recorded at the eastern margin. Although GNSS, INSAR, and geological data may partially differ, since they cover different time periods, they all indicate that the area is characterized by relatively low extensional deformation that is predominantly localized in the eastern part of Strymon basin. Spatially detailed information on the vertical motion component by InSAR indicates that relatively higher subsidence rates are limited within the quaternary deposits of the Strymon basin and predominantly towards the immediate hanging wall of the Serres fault zone. These correspond to localized patterns not easily attributed to tectonics, but mostly to groundwater extraction, while their temporal behavior that reflects the seasonal variability of the groundwater table indirectly confirms the above statement (Figure 10). Regarding the average horizontal motion of the study area, the V results are in accordance with the geodynamic regime of the broader Aegean region. In fact, the northmost Aegean region, where our study area belongs to, shows a slower ca. southward motion compared to the central and southern parts of the Aegean, where the velocity gradually, but also rapidly, increases. The V results show consistency with other geodetic investigations conducted in the wider Aegean region [7,14,107]. After correlating the geodetic strain parameters with the major active tectonic structures, it becomes clear that the highest extension occurs where the E-W-trending Serres fault and the NW-SE-trending Nea Zichni fault are located. Both structures are recognized as normal faults (Serres as a pure normal fault and Nea Zichni as a predominant normal fault with a possible minor strike-slip component). The Serres fault has a clear imprint on the topography, as well as in the hydrographic network. On the other hand, the Nea Zichni fault has also been studied through palaeoseismic trenching, confirming its Holocene activity and showing that deformation is widely distributed in several parallel strands. To a lesser but certain degree, geodetic analysis marks some tectonic activity at the western Strymon basin's margin. In particular, moderate values of geodetic parameters are documented in the northwestern part of the study area, south of Kerkini Lake and NW of the village of Zevgolatio. Within this area, a dense concentration of epicenters is also shown in Figure 1, completing the geodetic results. Until now, no active tectonic structures had been identified or mapped in this part of the Strymon basinal margin. Along the same margin, further to the southeast, NE-dipping marginal faults do occur. All evidence and indications suggest the northwestward continuation of the marginal faults up to Lake Kerkini with the missing 'Zevgolatio fault'. However, one may wonder whether these results and observations belong to an antithetic fault along the opposite side of the basin. The possibility of the occurrence of such a fault along the northeastern margin of the Strymon basin cannot be excluded; on the contrary, it is quite probable that the entire eastern margin of the basin, from Nea Zichni to Sidirokastro and the Belles fault zone, is tectonically controlled.