## 3 Seismotectonic Setting, Data Selection, and Analysis  
Intense seismic activity in the Central Ionian Islands of Cephalonia and Lefkas during the last few years, along with several large events (M > 6) over the last century [39; 40], clearly highlight the key role of this area in the kinematic process in the Eastern Mediterranean. The area is dominated by a major regional seismogenic zone known as the Cephalonia Transform Fault (CTF) (Figure 3), as well as several other faulting features, resulting in generation of the highest seismic energy release in Europe [41; 42]. The broader area is characterized by a complex kinematic and geodynamic regime. The area links the oceanic subduction boundary in the south to the collision between the Apulian microplate and Eurasia in the north [43; 44; 45]. This complicated tectonic regime creates a stress field that generates intense seismic activity and ground deformation on both a local and regional scale. Based on seismological data and geodetic measurements, the CTF zone is described as a dextral strike-slip faulting type system. This system is composed of two separate segments that run along the western shores of the Cephalonia and Lefkas Islands. The southern segment, offshore of Cephalonia, extends for approximately 90 km on a SW-NE direction and ends on the northern part of the island. The northern segment, offshore of western Lefkas Island, strikes a NE-SW direction for \(\sim\)50 km, ending close to north-western Cephalonia. This segment dips to the ESE and exhibits dextral strike-slip motion combined with a small thrust component [45]. Over the last twenty years, several strong earthquakes have devastated the islands of Lefkas and Cephalonia. In August 2003, a strong event (M\({}_{\rm w}\)6.3) occurred off-shore of the north-western coast of Lefkas Island [46; 47; 48; 49; 50]. In late January-early February 2014, two large-magnitude earthquakes (M\({}_{\rm w}\)5.9 and M\({}_{\rm w}\)6.1) were located in the western part of Cephalonia [51; 52]. However, these events were not linked directly with the CTF zone. This study focuses on a strong seismic event that took place in near proximity to the PONT continuous GNSS station. On 17 November 2015, a strong earthquake (M\({}_{\rm w}\)6.4) occurred in the southern part of Lefkas Island [53; 54] just north of Cephalonia. The main event was followed by a significant post-seismic activity that extended southwards towards Cephalonia. The hypocenter of this earthquake was located at a depth of \(\sim\)10 km, and the fault plane solutions demonstrated a NNE-SSW striking dextral strike-slip seismic fault with a reverse component that dipped east at a high angle of about 70\({}^{\circ}\)\(\pm\) 5\({}^{\circ}\). The after-shock seismic activity extended along three distinctive clusters north and south of the main event [54]. The northern cluster seemed to extends towards the epicentral area of the  
Figure 3: Map of the central Ionian islands of Lefkas, Cephalonia, and Ithaca, showing the main faulting zones and marking the continuous GNSS stations (triangles) PONT and SPAN in Lefkas and VLSM in Cephalonia islands. Circles represent the earthquake epicenters (M > 3) after the 17 November 2015 main event. Red and blue vectors represent the cGNSS horizontal velocities before and after the 2015 earthquake, respectively. Black arrows show the co-seismic deformation. CTF: Cephalonia Transform Fault. 2003 strong earthquake, the central one was located in the vicinity of the main event, while the southern one extended towards Cephalonia Island and about 15 km southwest of the epicenter. The spatial coverage of the aftershocks indicated less dense distribution close to the epicentral area, while away from the main shock, there was higher concentration of post-seismic activity.