Insight into the tectonostratigraphy of the historic Kefalonia island (Greece): a reflection seismic survey

Abstract. Kefalonia island, in front of the Greek west coast, is placed in a peculiar tectonic setting characterized by a transition from an oceanic subduction contact to a continental collision. This tectonic setting results in strong tectonic activities and seismicity in the area making the island a testbed for geological, geophysical, and archeological studies. To improve the subsurface knowledge and shed light in the top 100s of meters, we acquired three seismic profiles in the isthmus connecting the main part of the island to the Paliki peninsula, in the Thinia valley, where the presence of a possible channel has been disputed to make Paliki the Homer’s Ithaca (home of Odysseus). A total of approximately 3.5 km of seismic data was acquired using 5 m receiver and shot spacing and a 25 kg accelerated weight-drop as the main source. The sharp topographic changes and morphological features of the valley made the survey challenging, limiting the spread, precluding uniform shot points, and resulting in strongly crooked profiles. The acquired data, however, show visible reflections with variable quality down to 0.5 s and occasionally to 1 s. First-break traveltime tomography and 3D reflection traveltime modelling were performed to complement the seismic reflection processing work together with lithological columns from three boreholes present along the profiles. Results show a low-velocity zone with no reflectivity from the surface to approximately 100 m depth probably related to the presence of loose material, under which two main east-dipping reflections are imaged. With the help of surface geology and tectonic history of the valley, we interpret these features as the same lithological boundary displaced by three highly east-dipping thrust/reverse faults probably part of the Hellenide thrusts. These findings further constrain the local recent tectonic history and thus, the long-debated presence of an historic water channel in the valley.