## 4 Seismicity of the Southern Ionian Islands  
From the geotectonic point of view, the southern Ionian Islands are located in the external part of the Hellenic Arc and in the east of the Hellenic Trench, which represents the convergence boundary between the African and Eurasian plates, as it is shown in the  
Figure 2: Neetectonic maps of Cephalonia, Ithaki and Zakynthos Islands based on [PERSON] et al. [4, 5, 36] along with their fault blocks. Cephalonia: fault blocks of Erissos peninsula (EP), Paliki peninsula (PP), Aenos Mt (AM) and Argostoli peninsula (AP). Ithaki: fault blocks of northern, central and southern Ithaki (NI, MI and SI respectively). Zakynthos: fault blocks of northern Zakynthos (NZ), western part of central Zakynthos (WCZ), eastern part of central Zakynthos (ECZ), Keri (KR), southern Zakynthos (SZ) and Skopos Mt (SM).  
introductory figure. Thus, it constitutes one of the most seismically active parts in the Mediterranean region, in Europe and worldwide.  
The historical seismicity over the last 500 years is well documented for the southern Ionian Islands. Historical seismicity data indicates that these islands were struck by shallow earthquakes with magnitudes larger than 7.0 and maximum intensities larger than X [15; 17; 35; 37]. According to historical and recent seismicity data, large earthquakes in the southern part of the Ionian Sea are usually generated in couples (twin or cluster events) with the period of their occurrence varying from few days to 5 years [10; 38]. Characteristic examples of such events are the earthquakes of 1948 in Lefkada (22 April and 30 June) as well as the earthquakes of 1953 (9, 11 and 12 August), of 1983 (17 and 19 January and 23 March), and of 2014 (26 January and 3 February) in Cephalonia [17].  
As regards seismogenic sources in the southern Ionian Islands, earthquakes with magnitudes larger than 5.0 have been concentrated in several seismic zones comprising the western offshore Cephalonia and Lefkada areas, the Zakynthos channel and the respective structural basin between Zakynthos Island and Peloponnese and the area southwest of Zakynthos Island [15]. These seismic zones include significant seismic sources ofhigh productivity and the frequent occurrence of destructive earthquakes in both historical and recent times [39; 40].  
The prevailing seismogenic source in the study area is the Cephalonia Transform Fault Zone (CTFZ) (Figure 3). The CTFZ comprised two segments: (a) the Lefkada segment to the north, which is located offshore western Lefkada and (b) the Cephalonia segment to the south, which is located offshore western Cephalonia [1; 2; 3; 6; 7; 41].  
The Lefkada segment is a 40-km-long, NE-SW-striking and ESE-dipping fault, extending from the northwestern offshore part of Lefkada Island to the northern offshore part of Cephalonia Island [2; 42]. It is characterized by a dextral strike-slip motion along with a  
Figure 3: The epicenters of the 12 August 1953 (red star) along with the foreshocks on 9 August (yellow star) and on 11 August (orange star) and the aftershocks and associated events until the end of December 1953 (green circles) based on the earthquake catalogue of [PERSON] et al. [25]. Seismogenic sources are also presented based on the Greek Database of Seismogenic Sources by [PERSON] et al. [38]. The Cephalonia Transform Fault Zone is located offshore west of Lefkada and Cephalonia islands.  
small thrust component. The Cephalonia segment is a 90-km-long, NE-SW-striking and ESE-dipping fault, close to the western offshore part of the homonymous island [3; 6]. It constitutes the zone with the highest seismicity in the western part of the Hellenic Arc and Trench system [17; 33; 34; 37] including the August 1953 Ionian Sea earthquakes.