Tectonic Geodesy Synthesis and Review of the North Aegean Region, Based on the Strain Patterns of the North Aegean Sea, Strymon Basin and Thessalian Basin Case Studies  
first an approximate estimation then became a high-resolution, quantified proof of how the lithospheric plates move and deform. The first studies started in the 1990s (e.g., [1; 2]), and since then, the GPS/GNSS systems have been broadly used for monitoring geodynamics in various parts of the world. In the past several years, ground station hardware and analysis techniques have also significantly improved, making the acquisition and installation of the stations more attractive economically and the data processing more precise, leading to more realistic results. In this context, the spatial resolution has improved with the denser networks, while at the same time, the time windows have also become longer, permitting more extended periods of monitoring and more accurate observations. In the East Mediterranean, plate tectonics have created a complex geodynamic regime: the westward tectonic escape of the Anatolian microplate pushes the respective Aegean southwestwards, producing intense interplate deformation expressed by lithospheric-scale tectonic structures, and intraplate deformation, forming numerous crustal faults [3; 4]. The Hellenic Subduction Zone (HSZ), also known as the Hellenic Arc, and the North Anatolian Fault Zone (NAFZ) are the dominant interplate structures associated with the intense seismic activity. The key player in Aegean geodynamics is the 80 myr evolution of the Hellenic Arc, which migrated southwards to its current position with a simultaneous roll-back of the subducting slab ([5] and references therein). This procedure left room for the Anatolian plate to push the Aegean southwestwards through the North Anatolian Fault (NAF) and its western prolongation into the North Aegean Sea, i.e., the North Aegean Trough, generating a complex seismotectonic setting along the eastern Aegean Sea--western Anatolia (Figure 1). According to previous studies (e.g., [3; 6]), the Hellenic Trench has undergone a retreat (approx. 580 km) since the Eocene-Miocene [7; 8]. This geological phenomenon has resulted in a tectonic regime, which is characterized by N-S and NE-SW extensional occurrences in the Aegean and Anatolian regions [9; 10]. The southwest Anatolian microplate motion is considered to be related to the exertion of pulling and pushing forces resulting from the HSZ in its western part [5]. This movement is affecting the lithospheric thickness across Anatolia and the Aegean [11; 12]. The Hellenic Trench (HT) retreat results in the extensional stress field generation, causing the crustal thinning of central and northern Greece and western Anatolia ([13; 14] and references therein). In our study area (Figure 1), i.e., the northern Aegean, the North Aegean Trough (NAT) and the North Aegean Basin (NAB), two successive and interconnected tectonic structures dominate and affect a wide area of the North Aegean Sea as the western prolongation of the NAF ([15] and references therein). Specifically, these two tectonic structures cumulatively accommodate a dextral (right-lateral) motion of 24-30 mm/yr ([16] and references therein). The NAT fault zone exhibits quasi-pure shear characteristics, while the NAB region displays transtenasonal deformation [17]. Moreover, the smaller, less active, but evident, Central Aegean Trough (also known as the Skyros basin), which is the NAF's southern branch continuation [18; 19; 20], is the southmost transcurrent large structure in the Aegean Sea, affecting a large area bilaterally. Therefore, this area serves as a transitional zone that connects the strike-slip faulting observed along the NAF with the dip-slip, normal faulting, observed in the Greek mainland [21; 22]. In particular, the NAF and its continuation divides the lithosphere, while it is considered as the northern boundary of the Aegean--Anatolian microplates ([23] and references therein).