Reflection seismic imaging across the Thinia valley (Greece)

Abstract. Kefalonia island, in front of the Greek west coast, is located in a peculiar tectonic setting characterized by a transition from an oceanic subduction contact to a continental collision. This tectonic setting makes the island a test bed for geological, geophysical, and archaeological studies. To improve the subsurface knowledge and shed light in the top hundreds of metres, 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. A total of approximately 3.5 km of seismic data were acquired using a 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 crooked profiles. The acquired data, however, show visible reflections with variable quality down to 0.5 s and occasionally to 1 s. First-break travel time tomography and 3D reflection travel time modelling were performed to complement the seismic reflection processing work together with lithological columns from three boreholes located 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. Considering the surface geology and tectonic history of the valley, we interpret these reflections 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 contentious presence of a historic water channel in the valley.