Sea-Land correlation of the main seismogenic faults shaping the central Ionian Islands, Greece

The central Ionian Islands exhibit the highest seismogenic potential in the central Mediterranean and have therefore been extensively studied to mitigate the seismic risk. Despite numerous investigations over recent decades, the actual seismic hazard affecting the islands remains incompletely constrained.

The work was carried out within the framework of the internship project “Hazard assessment combining geological, geophysical and seismological data offshore Ionian Islands, Greece”, and aims to investigate the location and geometry of the main faults in the offshore area between Zakynthos and Cephalonia and to correlate offshore faults segments identified in the marine domain with their onshore counterparts. Particular attention is given to the Ionian Thrust and to the fault that was responsible for the destructive August 1953 earthquake that devastated Cephalonia Island.

We analyzed a comprehensive geophysical dataset acquired during two marine geophysical surveys: IONIANS 2022 (CNR project) and POSEIDON 2023 (Eurofleet+ project). The dataset includes three high-resolution and two high-penetration multichannel seismic profiles, several kilometers of TOPAS sub-bottom profiles and high-resolution swath bathymetry. Seismic interpretation allowed us to map the Ionian Thrust from south of Zakynthos to Cephalonia and its intersection with the main trace of the Cephalonia strike-slip fault. In the offshore domain, the Ionian Thrust is expressed as west-verging anticline with local transcurrent component. Moreover, in the narrow marine passage between Cephalonia and Zakynthos, we identified a west-verging anticline with transcurrent component which aligns well with the hypothesized epicenter of the 1953 earthquake.

Our interpretations were integrated and compared with existing geological and geophysical models from the literature, enabling the identification of the offshore continuations of fault systems responsible for several historical and instrumental seismic events. By further integrating offshore data with the onshore geology of both islands, we achieved a robust land–sea correlation of the dominant tectonic structure in the area, namely the Ionian Thrust.

Finally, the combined analysis of newly-identified tectonic structures and regional seismicity, allowed us to draw the position and trend of the seismogenic fault source of the 1953 earthquake as well as the active segments of the Ionian Thrust. These new findings strongly improve our understanding of the tectonic framework of the marine area surrounding the central Ionian Islands and provide crucial input for future seismic hazard modeling and risk assessment in this area of the western Hellenic Arc.