SEISMogenic behavIour of COntinental Subduction (SEISMI-COS): insights from rheology and petrophysics of Corsica blueschist and eclogite-facies continental units

Continental subduction is a fundamental stage in the tectonic evolution of convergent plate margins, accommodating the transition from oceanic subduction to continental collision and orogenic build up. Despite the elevated seismic hazard currently posed by destructive earthquakes in continental subduction settings (e.g., Taiwan 1999 Chi Chi M_W = 7.6, 2024 Hualien M_W = 7.4; Nepal 2015 Gorkha M_W = 7.8; Albania 2019 Durres M_W = 6.4), our understanding of the processes steering the seismogenic behaviour during prograde subduction of the buoyant, dry, quartzo-feldspathic continental lithosphere remains limited. With the Maria Skłodowska Curie Action SEISMI-COS, we aim at providing quantitative estimates of the stress state, rheology and petrophysical properties of natural deformation zones developed during progressive subduction of continental lithosphere. We will focus on fossil deformation zones exposed in the metamorphic units of Northern Corsica, where the former crystalline basement of the European continental margin has been coherently subducted to and exhumed from different depths during Eocene Alpine orogenesis. Different metamorphic units preserve pristine deformation structures developed at increasing subduction depth, making Northern Corsica the perfect natural laboratory to track the prograde rheological evolution and seismogenic behaviour of the subducted continental lithosphere from shallow seismogenic depths all the way down to conditions at intermediate-depth earthquakes are expected. Preliminary results show that units subducted at progressive depths show different structural features, from pseudotachylyte-bearing fault zones and brittle-ductile shear bands and veins in the outermost continental slices (Corte blueschist units), to high-pressure ductile shear zones (Tenda blueschist phyllonites) involving cycles of fluid pressure variation and veining (Centuri shear zones). This plethora of mesostructures represent the variable seismogenic behaviour during subduction of crystalline continental units subducted at different depths. Field, microstructural, and laboratory analyses will provide us with fundamental insights on how rheology and petrophysics control seismogenic deformation.