From shallow to very shallow image of the highly active Kefalonia - Zakynthos fault system

4 pages, 2 figuresIn May 2022 and June 2023 two oceanographic cruises were carried out around the Ionian Islands with the aim of defining the real geometry of the strike-slip fault system of Kefalonia and of the reverse faults present south of Zakynthos. The acquired multidisciplinary and multiresolution data will also allow to understand the dynamics of the area offshore the Peoloponnese peninsula, the deformation of the surface sediments at the transition of the two systems, i.e. from reverse fault system to strike-slip fault system, and the relationship between the recorded seismicity and mapped fault activity. To date, the analysis of the processed data has allowed us to define the tectonic and morphological complexity of the fault system affecting the investigated area. [...]Thanks to the CNR for supporting the cruise with time ship, IONIANS 2022 project. Interpretation of seismic profile has been done using the Kindgom IHS Markit. Poseidon project has been supported by Eurofleet+ SEA02_13_POSEIDONPeer reviewe

POSEIDON: New data on offshore structures in the west Peloponnese - Ionian Islands Domain and implications for seismic hazards

8th International Colloquium on Historical Earthquakes, Palaeo- Macroseismology and Seismotectonics, Past earthquakes and advances in seismology for informed risk decision-making, 17-20 September 2023, Lixouri, Kefalonia Island, Greece.-- 4 pages, 2 figuresOur cruise POSEIDON from 10 to 22 June 2023, on Research Vessel (R/V) Laura Bassi, aimed at mapping the tectonic structure of arguably one of the most complex and comparatively little evaluated regions, with demonstrated seismic hazard, in the Mediterranean. The region encompassing this tectonic domain extends from the western Peloponnese across the Ionian Islands (Figure 1). Here, a complex fault system with numerous strands has developed in a region with dramatic lateral changes in deformation rates. This system has produced numerous large earthquakes, mostly offshore, recorded during the past few decades in the onshore Greek national seismological network(Hadad et al., 2020). However, the large Cephalonia 1953 Mw~6.8 event (Stiros et al., 1994) was recorded in comparatively few stations only. This earthquake is possibly the most destructive seismic event in recent Greek history, causing the collapse of ~85% of all buildings on Kefalonia, ~1000 deaths, and ~145k people homeless, (Saranga, 2017; Hore, 2019). The limited data on the 1953 earthquake has made it poorly understoodcomparatively with more recent, albeit less destructive events. The epicentreof the 1953 event is poorly located, and the location and dimensions of the causative fault are unconstrained. Likewise, the thrust fault focal mechanism, located E or SE of Kefalonia, has a hypocenter depth poorly defined from <50 km to <20 km, depending on the analysis. Surface geology studies of the islands interpret active shallow thrusting(Underhill, 1989), and it has been proposed that the 1953 event ruptured several of those faults. The goal of POSEIDON is to determine region fault system structure and kinematics. [...]Peer reviewe