Résumé
An active submarine fault system, the North Alfeo fault, extends from the SE flank of Mount Etna, offshore Eastern Sicily 150 km to the SE. It is interpreted to be the primary surface expression of a lateral slab tear fault (a lithospheric scale fault which bounds the W edge of the subducting Ionian slab). Ultra-high-resolution micro-bathymetric data (1m grid-spacing) were acquired during the FocusX1 and FocusX2 cruises by the Remotely Operated Vehicle (ROV) Victor 6000 and by the Autonomous Underwater Vehicle (AUV) idefX at an altitude of 50 m above the seafloor. These data image the fine structure of a 16-km-long segment of a dextral strike-slip fault, marked locally by transpressive ridges and narrow lozenge shaped pull apart basins. A network of tightly-spaced N-S oriented normal faults is also observed throughout, most prominently on a triangular plateau, but also further south along the horse-tail termination of a NW-SE oriented splay fault of the Malta Escarpment. The N-S striking and steeply W dipping normal faults dissecting the triangular plateau are well imaged in chirp (sub-bottom) profiles acquired with the AUV. Analog modeling using granular materials tested a range of boundary conditions (layer thickness, pre-existing plateaus above the fault trace, an oblique fault with respect to a step in the morphology, a 15 degrees change in orientation of the fault orientation below the layer of granular material, etc.). Certain large-scale features observed in the natural example can be reproduced; e.g. - regularly spaced transpressive ridges with 30 degrees oblique fault splays (clockwise with respect to the fault trace at depth) and an imbricated pop-up within a larger transpressive plateau. Other features, like the pervasive N-S oriented domino faults are not easily reproduced. Their characteristic spacing (about 150 m) implies the presence of a shallow detachment for these structures, probably < or =1 km.