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Deep view of the Subduction-Transform Edge Propagator (STEP) fault in the Calabrian Subduction Zone
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Abstract
The Calabrian Subduction Zone plays a key role in the evolution of the central Mediterranean in the framework of
the convergence between Africa and Europe.
Here, the remnants of the World’s oldest oceanic crust form a narrow NW-dipping slab passively subducting
beneath the Calabrian Arc.
Recently published high-resolution seismic profiles and bathymetric data of the western Ionian Sea highlight
the presence of a NNW-SSE faulting system connected with a series of Plio-Pleistocene syn-tectonic basins.
These features are correlated with the recent activity of a major NNW-SSE deformation zone confining the active
subduction to the SW and interpreted as a Subduction-Transform Edge Propagator (STEP) fault.
The goal of this work is to jointly reconstruct the geometry of the STEP fault and the subduction interface in its
surroundings.We use multichannel seismic profiles acquired in the southwestern part of the Calabrian accretionary
wedge to focus on the STEP fault geometry at depth and to analyse its relationships with shallow deformation
features.
The quantitative analysis and enhancement of seismic data provided an accurate image of the internal structure
of the accretionary wedge at various depths, showing growth strata in the Plio-Pleistocene succession and major
discontinuities in the lower crust.
Our results depict a main subvertical, slightly east-dipping, lithospheric fault cutting the oceanic crust down to
the Moho, and a rich set of associated secondary synthetic and antithetic faults. This picture also provides new
insights on the STEP fault propagation mechanism.
In addition, the tridimensional correlation of the STEP fault occurrences in various seismic profiles provides
a preliminary scheme of its segmentation and highlights the relationships of this master fault with other main
structural elements of the Calabrian Arc and Eastern Sicily, including some of the faults deemed to be responsible
for major historical earthquakes in the area