## 4 Discussion
### The Broad Ionian Sea Area  
The overall image of the seismic activity in the broad area of Ionian Islands is dominated by the three seismic sequences generated after the large-magnitude events (\(M>6\)) in Cephalonia, Lefkada and Zakynthos Islands (Figures 2 and 3). The Lefkada sequence is mainly aligned and concentrated along the north Lefkada segment of the regional CLTFZ structure, expanding offshore and west of the northern part of Cephalonia. The 2014 Cephalonia sequence occurred on a local faulting zone, associated with the Cephalonia segment of the CLTFZ but not comprising part of it. It is distributed spatially on a wider zone, along the western Paliki peninsula, and extends offshore, west of the northern Erissos peninsula. These two sequences appear to be coupled to each other in both time and space and linked with the earlier 2003 Lefkada earthquake. The southern Zakynthos sequence also has regional characteristics and is spatially distributed in a region much larger than anticipated for the magnitude of the mainshock [29]. This is an area affected by the transition of the northwestern end of the Hellenic Arc subduction zone to the CLTFZ major faulting structure. The geodetic data clearly depicted the kinematic pattern of the broad area, with respect to major tectonic formations and seismic activity (Figure 11). Comparing the regional velocity field on the northern Ionian Islands with the one of the central islands, a clear kinematic boundary emerges between these two areas. The northern islands show a uniform motional pattern, while the velocity field at the central and southern Ionian Sea shows a clockwise rotation around an axis located on Cephalonia Island (calculating the horizontal velocities with respect to VLSM station). Based on the results of this study, a rotation rate of 6.9 \(\pm\) 2.1 degrees/Myr was estimated. This agrees with previous regional studies [92; 93], as well as with local geodetic studies on Cephalonia [13]. Baseline changes between several GNSS sites reveal the extensional regime along the Ionian Islands, which is gradually reduced from north to south, while compression occurs between the central Ionian Islands, and western Greece and the Peloponnese. Extension is also observed between western Greece and the Peloponnese, as well as across the NW Peloponnese. The strain regime alternates the periods after the strong earthquakes, marking the post-seismic relaxation process. The spatial extension of the co-seismic displacements reflects the regional or local character of the activated area. The Lefkada and Zakynthos earthquakescaused static displacement in the broad area, while the Cephalonia events affected only the local GNSS sites. The temporal and spatial joint analysis of the seismological and geodetic data revealed that the 2014 and 2015 seismic sequences are connected, while the Zakynthos one is part of the tectonic process in the western termination of the Hellenic subduction margin. The expansion of the seismic activity after the 2014 and 2015 events offshore of northern Cephalonia is the spatial link. In this area, previous work [52] identified a seismic gap, indicating that a segment of the CLTFZ has not ruptured yet and may generate a strong event in the future. The present analysis shows that seismicity in this region is clustered in a large number of small segments oriented almost in an E-W direction, transverse to the axis of the CLTFZ. The latter may indicate the transition between the Cephalonia and Lefkada segments of CLTFZ, and the increased seismicity may relieve the accumulated stress. Thus, the occurrence of a strong event in this region seems less likely, but cannot be excluded. Meanwhile, the area between Cephalonia and Zakynthos is characterized by low seismic activity. It is a region whose kinematic status is affected by the CLTFZ in the north and the subduction process in the south.