###### Abstract
Lastly, at the southernmost part of the Administrative Region of Attica, and quite remote from the mainland, the islands of Kythira and Antikythira have been mainly affected by earthquakes related to the Hellenic subduction. Some notable historical events include the 1717 CE, M = 7.0 one in Crete, with I = VIII, which had a significant impact on the islands of Kythira and Antikythira; the 7 June 1750, M = 7.2 one at Kythira, with I = IX, preceded by another strong earthquake on 12 May; and the 29 June 1798, M = 6.4 one at Kythira, with I = VIII [2]. Also of great importance for this area was the 21 July 365 CE earthquake of Crete, with an estimated magnitude of 8.3-8.5 [2; 27], which caused a devastating tsunami [28; 29]. In the instrumental era, an M = 7.6 event occurred on 11 August 1903 at 04:32:54 UTC, with the epicenter at the northern part of Kythira at a focal depth of 120 km, with I = IX [2]. The most recent significant earthquake in this area was the 8 January 2006, M\({}_{\rm w}\) = 6.5 event, which occurred at a focal depth of 58 km, about 10 km east of Kythira [4]. The earthquake was felt in Attica's mainland and in neighboring countries (Italy, Turkey, Egypt, Cyprus, Israel, Syria, Jordan, and Lebanon) but did not cause significant damage due to its large depth [30]. These intermediate-depth earthquakes near Kythira are mainly associated with either (oblique-) reverse or strike-slip faulting. The Attica region consists of continental and island areas belonging to different parts of the Hellenic Arc. More specifically, Kythira and Antikythira are located at the southwest Hellenic forearc, whereas Attica, with the Athens metropolitan region, belongs to the back-arc area. They present differences in their geological structure, including the participation of geotectonic units of the Internal Carbonate Platform in the geological structure of Attica, which are absent from the southern island part of the region, where the geotectonic units of the External Carbonate Platform and the Pindos Oceanic Basin predominate [31]. Their neotectonic structure, however, is characterized by the presence of active faults [32; 33; 34; 35; 36; 37; 38; 39; 40; 41], which have the potential to produce earthquakes with magnitudes equal to or greater than M\({}_{\rm w}\) = 6.0 [42; 43; 44] with significant impact on elements of the natural and built environment. Typical examples of such onshore active faults in the continental part of the Attica region have been mapped in the framework of multiparametric surveys [34; 39; 43; 45; 46]. In the insular part of the Attica region, onshore active structures are located on the islands of Salamina [35; 36] and Aegina, located in the Saronic Gulf, and on Kythira and Antikythira Islands in the south [40; 41; 45]. The common characteristics of these active structures refer to their spatial distribution and kinematics. They are normal to oblique-normal faults, as in some of them the contribution of the horizontal component in the movement of the fault zones is significant. They have formed mostly along the margins of neotectonic macrostructures (horsts and grabens) and delineate Neogene and Quaternary deposits that have filled the post-alpine basins. They are clearly observed either as impressive best-preserved mirror-like fault surfaces or through well-preserved morphological discontinuities of tectonic origin. They have greatly controlled the formation and evolution of secondary tectonic landforms, such as the drainage networks showing steep bends under the influence of active faults, selective flow paths under the synergy of active tectonics and lithology, asymmetries in development with respect to the main branch due to tilting of fault blocks, and intense incision along branches developing transversely to active faults due to tectonic uplift. As has been deduced from studies on the type and distribution of earthquake environmental effects and building damage, marginal fault zones have controlled the distribution of these phenomena [9; 32; 39; 46].