Seismological and Ground Deformation Study of the Ionian Islands (W. Greece) during 2014–2018, a Period of Intense Seismic Activity

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 PGV expected values in the central Ionian.

Earthquake-Induced Tsunamis in Western Greece (Ionian Sea and Western and Southern Peloponnese): Use of Tsunami Quantities, Impact and ITIS-2012 Intensities for Highlighting Susceptible Areas

“…The Ionian Islands in western Greece are defined by high seismicity characterized by frequent strong and destructive seismic events resulting in intense ground deformation [24], extensive environmental effects of earthquakes [25][26][27][28][29]31] and building damage [71][72][73]. This intense seismicity is mainly attributed to the NNE-SSW-trending, right-lateral Cephalonia-Lefkada Transform Fault Zone (CLTFZ) which is located at offshore western Cephalonia and Lefkada [24,[74][75][76][77].…”

“…The Ionian Islands in western Greece are defined by high seismicity characterized by frequent strong and destructive seismic events resulting in intense ground deformation [24], extensive environmental effects of earthquakes [25][26][27][28][29]31] and building damage [71][72][73]. This intense seismicity is mainly attributed to the NNE-SSW-trending, right-lateral Cephalonia-Lefkada Transform Fault Zone (CLTFZ) which is located at offshore western Cephalonia and Lefkada [24,[74][75][76][77]. The CLTFZ constitutes a major boundary in the kinematic field of the region as it separates the Ionian margin into two parts with different kinematic and seismological properties: the northern part comprises the northern Ionian ITIS-2012 is a 12-grade scale ranging from I (not felt) to XII (completely devastating) that benefited mainly from the collection of large datasets following the two great tsunami events in 2004 and 2011 (Boxing Day 2004 Indonesian tsunami and 11 March 2011 Japan tsunami) and from other significant contemporary and historical events which were also taken into account [34].…”

“…The Ionian Islands in western Greece are defined by high seismicity characterized by frequent strong and destructive seismic events resulting in intense ground deformation [24], extensive environmental effects of earthquakes [25][26][27][28][29]31] and building damage [71][72][73]. This intense seismicity is mainly attributed to the NNE-SSW-trending, rightlateral Cephalonia-Lefkada Transform Fault Zone (CLTFZ) which is located at offshore western Cephalonia and Lefkada [24,[74][75][76][77]. The CLTFZ constitutes a major boundary in the kinematic field of the region as it separates the Ionian margin into two parts with different kinematic and seismological properties: the northern part comprises the northern Ionian Islands (the Diapontia, Corfu, Paxi and Antipaxi Islands), which are moving slowly northward and northwestward at rates lower than 5 mm/year with respect to Eurasia, and the southern part comprises the Lefkada, Cephalonia, Ithaki and Zakynthos Islands, which are moving rapidly southwestward at rates ranging from 6 to 30 mm/year [78][79][80].…”

“…Increased seismicity has been reported over the past decade, particularly between 2014 and 2018, with strong earthquakes with M > 6.0 shocking the central Ionian Islands. Early in 2014, two earthquakes (Mw = 6.1 and Mw = 5.9) struck Cephalonia Island, while in November 2015 and October 2018, two earthquakes with Mw = 6.4 and Mw = 6.7 struck the southern part of Lefkada and offshore southern Zakynthos, respectively [24], with extensive environmental effects [25][26][27][28].…”

“…One such area is the western part of Greece including the Ionian Islands and the Ionian coast of Peloponnese (Figure 1). This is a region of high seismicity, including the occurrence of strong and destructive earthquakes, both recently and during the historical period [24]. These earthquakes, some of which are among the most powerful and destructive not only in Greece but also in the Eastern Mediterranean, are characterized by the clear prevalence of horizontal slip with a small contribution of either the normal or the reverse component of the movement [24].…”