## 2 Geodynamic Setting and Tectonic Pattern
The North Aegean Basin (NAB) and the North Aegean Trough (NAT) comprise the northern strand of the North Anatolian Fault (NAF), while the Central Aegean Trough represents the corresponding southern strand. The Corinth Gulf (CG) is the most extensionally growing region in the Aegean. In the Ionian Sea, the Apulian-Aegean Collision Zone (AACZ) is shown to the north and the Hellenic Arc to the south, separated and displaced by the right-lateral Cephalonia Transfer Fault Zone (CTFZ) in the middle. Hatched areas represent extension. Moment tensor solutions since 1997 from the RCMT catalogue [69] are also shown. The white rectangle indicates the location of the inset map (c). (e) Hillshade map showing the active/Neotectonic faults of the study area (F = Fault, FZ = Fault Zone). Recent earthquake spatial distribution (M\({}_{\rm L}\geq\) 0.5) since 2008 by the Institute of Geodynamics, National Observatory of Athens (IG-NOA), is also shown. Tectonic strain is partitioned among the active faults of the study area; therefore, a holistic approach studying strain should incorporate the active structures. Overall, major fault zones in the study area are striking both E-W (Sochos, Drama, etc.) and NW-SE (e.g., Symvoli-Fotolivos, Tholos-Nea Zichni), which is in agreement with the palaeoseismic results [45]. The most important known fault zones in our study area are:  
1. The Symvoli-Fotolivos fault zone  
The Symvoli-Fotolivos fault zone (SFFZ) is a NW-SE-striking normal fault zone, dipping to the NE, forming the Drama-Phillipi basin western margin. It is approx. 53 km long and comprises several fault segments. Palaeoseismic trenching, supported with radiometric dating, revealed that: (i) the fault plane dips at 55\({}^{\circ}\) towards NE (052\({}^{\circ}\)), in agreement with the strike of the fault zone extracted from the surficial geological and geomorphological mapping, and (ii) it is Holocene active, but with low slip-rate (0.14 mm/yr) and, hence, long earthquake recurrence intervals in the order of several thousands of years [45]. No major historically or instrumentally recorded earthquakes can be correlated with this fault, most probably due to its long recurrence interval. 2. The Tholos-Nea Zichni fault zone  
The Tholos-Nea Zichni (TNFZ) is a NW-SE-trending major normal fault zone that dips and downthrows to the northwest (225\({}^{\circ}\)), forming the eastern boundary of the Strymon basin [45]. The area bounded by the two fault zones (TNFZ and SFFZ) comprises of Alpine Mesozoic metasediments, which are unconformably overlain by Neogene fluvial and lacustrine deposits. The TNFZ displays common tectonic geomorphology features such as a relatively linear topographic boundary, inverted wine-glass valleys, and highly incised catchments that result from footwall uplift (e.g., Figure 2). Moreover, the direction differentiation of the ongoing extension, as well as the fault strike, may indicate that a limited horizontal component may occur. According to recent geodetic studies [58], a sinistral lateral component of motion is proposed. No significant events have been recorded instrumentally near the fault (e.g., all events were below M = 5.0). Only one strong historical event (M\(\sim\)6.8), which occurred in AD 597, has been recorded a couple of tens of km from the fault into its hanging wall, where the maximum subsidence is expected. This event changed the flow of the Strymon River near Amphipoli [70]. Therefore, this fault is one of the few candidates (possibly the most proximal one) that could have hosted this event. Palaeoseismic trenching, supported with radiometric dating, revealed that this is a Holocene active complex fault zone, with its deformation distributed across several synthetic and antithetic planes, and is interpreted as having a low slip-rate fault (0.20 \(\pm\) 0.1 mm/yr), with recurrence intervals in the order of 2500 \(\pm\) 1000 yrs [45]. 3.