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

Vassilis Sakkas,Danai Kazantzidou-Firtinidou,Vasilis Kapetanidis,Ioannis Spingos,Efthymis Lekkas,Spyridon Mavroulis,Ioannis Kassaras,Emmanuel Vassilakis,John D Alexopoulos,Spyridon Dilalos,Nicholas Voulgaris,George Kaviris,Evelina Kotsi,Gerasimos Tselentis,Michalis Diakakis

doi:10.3390/app12052331

Vassilis Sakkas, Danai Kazantzidou-Firtinidou + Show 13 more

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https://doi.org/10.3390/app12052331

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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.

Highlights

Epicenters in Lefkada and Cephalonia are linked to local faults and mainly to the Cephalonia–Lefkada Transform Fault Zone (CLTFZ), whereas seismicity offshore and close to Zakynthos is related to the border between the Eurasian and African plates
The high seismicity rate is reflected in the high seismic hazard of the central Ionian Islands that belong to the highest category (Zone III) of the current Greek Building Code, with a Peak Ground
Seismological analysis and geodetic results from continuous Global Navigation Satellite System (GNSS) stations were combined to study the spatiotemporal evolution of seismic activity and ground deformation in the Ionian Islands during the period from 2014 to 2018, characterized by the occurrence of strong earthquakes in Cephalonia, Lefkada and Zakynthos Islands

Summary

Introduction

The area of the Ionian Islands in western Greece plays an important role in the kinematic processes of the eastern Mediterranean. This tectonically complex area is by far the most seismically active region in Greece and among the most seismogenic regions in Europe. It is characterized by the frequent occurrence of destructive large earthquakes and undergoes intense ground deformation.

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