## 3 Materials and Methods  
In this paper we exploit the strain results of three regional GPS/GNSS studies, which focus on three neighbouring areas [17; 71; 72]: (i) the North Aegean Sea, (ii) the Strymon basin, and (iii) the Thessalian basin. The three case studies combined can give a wider understanding of the geodynamics of the northern Aegean crustal regime. The reasons for using these results are (i) the number of the GPS/GNSS stations, (ii) the long time-period of seven years, and (iii) the consistency of the used methodology. Next, we will briefly describe the technical features and the methodological procedure, which the three case studies rely on. Implementing permanent GPS/GNSS stations to acquire geodetic raw datasets is a dependable technique for the instrumental evaluation of deformation in the upper crust. The geodetic velocities have been predominantly employed, previously computed for Greece [73]. This paper focuses on combining the results of three study areas (North Aegean Sea, Strymon basin and Thessalian basin), which are uniformly monitored by 32, 16 and 27 GPS/GNSS stations, respectively. The stations mentioned above are incorporated within the five existing, continuously operating networks, namely HxGN/SmartNet Greece, Hepos, NoaNet, EUREF Permanent Network--EPN, and HermesNet, as documented [74]. This integration facilitates the combination of diverse datasets, thereby enabling the computation of more precise outcomes. The abovementioned geodetic velocities were measured over seven consecutive years, specifically from 2008 to 2014 (Figure 3). Continuous 24 h region monitoring was performed over a period of seven years, with a recording interval of 30 s. It is worth noting that the GPS/GNSS data rate is 1 HZ, which is decimated to 30 s, as mentioned above. Additionally, the geodetic velocities are referenced to the European Terrestrial Reference Frame 2000 (ETRF2000), which assumes the stability of the Eurasian plate. Furthermore, it is necessary to mention that GPS/GNSS stations provide reliable information related to horizontal motions. Therefore, this paper focuses on estimating strain derived from these motions. On the contrary, the vertical displacements recorded by the GPS/GNSS stations show great errors and hence cannot be considered for the strain analysis. The geodetic data processing considers the principles employed by European centres, wherein the Vienna Mapping Function 1 (VMF1; [75]) is executed to derive the Zenith Total Delay (ZTD) over a 2 h time interval. Furthermore, the extended analysis was conducted utilizing the IERS2003 conventions, and the geodetic raw datasets were analysed using the GAMIT/GLOBK software suite (version 10.5, Massachusetts Institute of Technology, Cambridge, MA, USA; [76; 77]). Based on all the above, the geodetic data yielded the estimation of every GPS/GNSS station's east and north velocity components and their respective errors. Several authors have widely implemented the triangulation methodology [78; 79; 80; 81; 82; 83], which is regarded as the most appropriate among various methodologies (e.g., least square methodology, etc.) for processing these datasets. The fundamental theory of the triangulation methodology involves the combination of the velocity components, along with their respective errors, taken each time from three different GPS/GNSS stations, which form the vertices of a triangle; at the barycentre (centroid) of each triangle, the overall velocity is calculated and the deformation processing starts, resulting in the strain parameters estimation [17; 72; 84]. A total of 404 triangles with their respective centroids were constructed for the North Aegean Sea, 216 for the Strymon basin, and 193 for the Thessalian basin, respectively. The strain parameters for each centroid were estimated using the 'GPS triangular calculator' software (UNAVCO, Boulder, CO, USA; [85]).