POSEIDON Seismic Hazard in the west Peloponnese - Ionian Islands DomainN

POSEIDON aims at studying arguably one of the most complex and comparatively little evaluated regions with demonstrated seismic hazard in the Mediterranean: The western Peloponnese & Ionian Islands tectonic domain. Here, a complex fault system occurs across an area with a dramatic change in deformation rates near the end of the Hellenic subduction zone. The fault system produces numerous large earthquakes, mostly offshore, recorded in the onshore Greek seismological network. Some events are poorly known, like the Cephalonia 1953 Mw~6.8 event, possibly the most destructive earthquake in recent Greek history. The 1953 event caused the collapse of 85% of all buildings on Cephalonia, ~1000 deaths, and ~145k homeless, and initiated a long-term population migration affecting the local economy, that has only recently started to heal. The earthquake was recorded in few stations: a poorly located epicenter, with the causative fault disputable.

A thrust fault focal mechanism E-SE of Cephalonia has a hypocenter between <50 km to <20 km depth, depending on the analysis. However, geology studies on the islands propose active shallow thrusting ruptured by the 1953 event. The scarce modern bathymetry indicates complex fault kinematics. Further, the upper-crust fault system occurs above the mega-thrust fault of the Hellenic subduction zone, inferred to dip NE at ~25-40 km depth. The transition from the upper-crust seismogenic zone to the mega-thrust is not understood. We infer that POSEIDON research region develops above the edge of the subducting slab, which is bounded to the NW by a tear.

In order to study the early stages of a Subduction-Transform Edge Propagator (STEP) fault system, POSEIDON aims are threefold and will A) Answer major open issues regarding faulting and natural hazards in the region, B) Address fundamental questions of earthquake phenomena, and C) Expand understanding in basic research related to subduction systems and STEP evolution.