###### Abstract  
Seismicity in the Ionian Sea (W. Greece) is mainly generated along the Cephalonia-Lefkada Transform Fault Zone (CLTFZ) in the central Ionian, and on the northwestern termination of the Hellenic subduction margin in the south. Joint pre-, co- and post-seismic ground deformation and seismological analysis is performed at the broad Ionian area, aiming to homogeneously study the spatiotemporal evolution of the activity prior to and after the occurrence of strong (\(M>6\)) earthquakes during the period of 2014-2018. The 2014 Cephalonia earthquakes (Mw6.1 and Mw5.9) were generated on a faulting system adjacent to CLTFZ, causing local ground deformation. The post-seismic sequence is coupled in space and time with the 2015 Lefkada earthquake (Mw6.4), which occurred on the Lefkada segment of the CLTFZ. Co-seismic displacement was recorded in the broader area. Seismicity was concentrated along the CLTFZ, while its temporal evolution lasted for several months. The 2018 Zakynthos earthquake (Mw6.7) caused regional deformation and alterations on the near-velocity field, with the seismicity rate remaining above background levels until the end of 2021. In the northern Ionian, convergence between the Apulian platform and the Hellenic foreland occurs, exhibiting low seismicity. Seismic hazard assessment revealed high PGA and FGV expected values in the central Ionian. I o  
The Ionian Sea (Figure 1) hosts areas with different fault geometries and kinematics. The prevailing tectonic structure is the NNE-SSW-trending, right-lateral Cephalonia-Lefkada Transform Fault Zone (CLTFZ), which is the most seismically active structure not only in the Ionian Sea, but also in Greece. This zone is a major boundary in the kinematic field of the region, as it separates the Ionian Margin into two different areas. The North Ionian Islands, comprising the Diapontia Islands, Corfu, Paxoi and Antipaxoi Islands, move slowly northward and northwestward at rates lower than 5 mm/year with respect to Eurasia. The South Ionian Islands, comprising Lefkada, Cephalonia, Ithaca and Zakynthos, move rapidly southwestward with velocities of 6-30 mm/year [1; 2; 3]. The CLTFZ is composed of two segments: the 40 km-long, NE-SW-striking, ESE-dipping, right-lateral Lefkada segment, extending from the northwestern offshore part of Lefkada Island to the northern offshore part of Cephalonia Island [4; 5], and the 90-km-long Cephalonia segment, close to the western offshore part of Cephalonia, with similar geometry and kinematic properties to the other segment [6; 7]. The South Ionian Islands (Zakynthos and Strofades) are located close to the northwesternmost tip of the Hellenic Arc, a few kilometers east of the Hellenic Trench in the southern Ionian Sea. The trench represents the active plate boundary where the eastern Mediterranean lithosphere is being subducted beneath the Aegean one. This subduction zone terminates against the Cephalonia segment of the CLTFZ. Figure 1: Seismotectonic background of the Ionian Islands region. Focal mechanisms of stronger events (\(M\geq 5.5\)) are presented (see Data Availability Statement for references). Historic seismicity is presented by gray squares (SHEEC database, [8; 9]) Principal stress axes \(\mathbf{S}_{1}\) (blue) and \(\mathbf{S}_{3}\) (red) after [10]. Fault lines after [11; 12; 13; 14; 15; 16; 17; 18; 19]. CLTFZ: Cephalonia–Lefkada Transform Fault Zone, WAFZ: Western Achaia Fault Zone. The CLTFZ is not the only major right-lateral fault zone in the Ionian Sea. A few kilometers south of Zakynthos, another structure occurs. It constitutes the southward extension of the seismic NE-SW-striking, right-lateral Western Achaia Fault Zone (WAFZ), which extends from the northwestern part of the Peloponnese to offshore southern Zakynthos [20]. The epicenter of the 8 June 2008, Mw6.4 Andravida earthquake [21,22] and its aftershock sequence were distributed along the onshore part of the WAFZ, at the northwestern part of the Peloponnese.