LEKKAS, E., MAVROULIS, S., ALEXOUDI, V. (2014). - The geodynamic and seismotectonic setting of Cephalonia (Ionian Sea, Western Greece) as factor controlling the distribution of earthquake environmental effects and structural damage induced by early 2014 earthquakes (January 26th and February 3rd, Mw 6.0). International Workshop on Seismic Hazard and Earthquake Engineering, TEI Ιονίων Νήσων, Αργοστόλι, abs
Cephalonia is the largest of the Ionian Islands in Western Greece and is located on the tectonic front of the Hellenic thrust and fold belt developed only a few km east of the Hellenic Trench representing an active plate boundary where the Eastern Mediterranean lithosphere is being subducted beneath the Aegean one. The subduction zone terminates against the Cephalonia Transform Fault Zone connecting the subduction boundary to the continental collision between the Apulian microplate and the Hellenic foreland and playing a significant role in the region's geodynamic complexity.
Historical seismic data indicate that Cephalonia has been repeatedly struck by moderate and strong, shallow earthquakes producing large seismic intensities and causing a large number of human casualties and great economic losses. One more episode in the geodynamic evolution of the island is the early 2014 earthquake sequence comprising two main shocks with the same magnitude (Mw 6.0) occurring successively in short time (January 26th and February 3rd) and space (neotectonic macrostructure of Paliki peninsula in the western part of Cephalonia). According to geological data collected in the field during our reconnaissance immediately after both earthquakes, it is concluded that each earthquake was induced by the rupture of a different pre-existing active fault zone located in Paliki peninsula. Strike-slip displacement can be inferred from the co-seismic surface rupture structures induced by both earthquakes. This coincides with the focal mechanism solutions provided by national and international seismological institutes.
Both earthquakes produced extensive earthquake environmental effects (EEE) mainly in the neotectonic macrostructures of the western Cephalonia and especially in Paliki peninsula, the western part of Aenos Mt and the northern part of Argostoli peninsula. The EEE are classified into primary and secondary. The primary EEE include displacements of tectonic origin (uplift and subsidence) and surface ruptures. The secondary EEE include ground cracks, slope movements, liquefaction phenomena and hydrological anomalies.
The western part of Cephalonia and particularly Paliki peninsula suffered the most damage during both earthquakes. Structural damage was observed in masonry and reinforced concrete (R/C) buildings, monumental structures including monasteries, churches and cemeteries, as well as stonewalls, road network infrastructures and port facilities.
The majority of the buildings constructed with strict earthquake standards after the catastrophic 1953 Cephalonia earthquake sequence showed good performance during both earthquakes since none of them collapsed and no resident was killed or seriously injured. This fact becomes even more important, if we consider that the peak ground acceleration values recorded during both earthquakes are among the largest measured so far in Greece.
The analysis and the comparison of all available data indicates that there is a strong correlation among the pre-existing active fault zones, the detected displacement discontinuities and the spatial distribution of the EEE and structural damage.