## 2 Tectonic Setting  
The Aegean region exhibits seismotectonic complexity, with the dominance of the subduction of the Eastern Mediterranean oceanic lithosphere beneath the Eurasian continental lithospheric plate in the southern Aegean Sea. This process forms the Hellenic Arc and its extensional back arc Aegean area [22] due to the slab roll back [23]. The Hellenic Arc is bounded to its northwestern edge by the right-lateral Kefalonia Transform Fault Zone (KTFZ) and to its southeastern edge by the left-lateral Rhoades Transform Fault (RTF). To the north of KTFZ, the continental collision of the Adriatic microplate and the Eurasia plate takes place, resulting in a compressional seismic zone running parallel both onshore and offshore to the western coastal areas of Greece and Albania. The westward motion of Anatolia as a rigid block results in the formation of the right lateral North Anatolian Fault Zone (NAFZ) extending through the Marmara Sea into the northern Aegean Sea along the North Aegean Trough (NAT), which is the boundary between the Eurasian plate and the Aegean microplate [24] (Figure 1). The available focal mechanisms of the Global Centroid Moment Tensor (Global CMT; Available online: www.globalcmt.org (accessed on 30 April 2022)) since 1976 highlighted that the vast amount of seismicity is associated with the above-mentioned and fast deformed active boundaries (Figure 1). Specifically, it is derived that the majority of the thrust fault  
Figure 1: The major active boundaries (solid yellow lines) and their relative motions (red arrows) in the broader Aegean Sea area, along with the available focal mechanisms of earthquakes that occurred since 1976 as derived from the Global CMT database (Available online: www.globalcmt.org (last accessed on 30 April 2022)). Fault plane solutions are shown as equal area lower hemisphere projection (compressional quadrants are depicted in red). plane solutions (fps) are concentrated in the proximity of continental collision of the Adriatic microplate and Eurasia in northwest Greece and along the Hellenic Subduction Zone active boundaries. The right lateral KTFZ and NATFZ are related to strike-slip fault plane solutions, and to a lesser extent in the southeastern Aegean area, where the left-lateral Rhoades Transform Fault is activated. Fast extension in N-S direction dominates in the back arc area, along with an E-W extension in the transition zone running parallel to both continental collision and oceanic subduction. The spatial extension of the active boundaries, along with the available fault plane solutions allow the definition of seismic zones with distinctive seismotectonic properties in the study area, and then the detection of the appropriate \(M_{thr}\) above which the temporal crossover between correlated and statistically independent earthquakes is seeking. The 10 sub-areas that are defined, based on the aforementioned criteria, are shown in the map of Figure 2 (red polygons), along with the \(M_{w}\geq 4.1\) crustal (\(h\leq 40\) km) seismicity covering the time period 1975-2021. The compressional stress field of western Greece and Albania constitutes the sub-area 1, in which seismicity is concentrated along the main low angle thrust faulting structures with an NW-SE strike parallel to the coast [24] and the corresponding P-axes to be generally oriented perpendicular to the collision front (Figure 1). The dextral strike-slip KTFZ is the sub-area 2. KTFZ is a well-defined fault zone characterized by right-lateral faulting with a considerable thrust component [25]. It consists of the most active fault zone in Greece with the frequent occurrence of large (\(M_{w}\geq 6.0\)) earthquakes. Figure 2: Epicentral distribution of Greek seismicity with \(M_{w}\geq 4.1\) since 1975. Each different color illustrates the earthquakes of the 10 distinctive sub-areas that the broader Aegean region is divided (the borders of each sub-area are denoted with red polygons).