The Sicilian Channel: fault geometry and tectonic structures, 3D, analogue and numerical modelling, geodynamic mechanism. Consequences for seismic hazard assessment.

Analysis of multichannel seismic reflection profiles acquired in the northern part of the Sicilian Channel allows a 3D reconstruction of a NS-trending tectonic lineament which displays a mainly transcurrent structural character and it is constituted of two major strike-slip faults. The western fault (Capo Granitola Fault) does not show clear evidence of present-day tectonic activity and toward the south, the NS-trending tectonic lineament merges into the Graham Bank. The eastern fault (Sciacca Fault) is structurally more complex, showing active deformation at the sea-floor, particularly evident along the Nerita Bank. The Sciacca Fault is constituted of a primary fault and splay faults compatible with right-lateral kinematics. A set of analogue models has been carried out to better constrain the tectonic processes that led to the structural setting seen from seismic data. Complex right-lateral structure and uplift/subsidence patterns generated by the models are compatible with the 3D model obtained from seismic reflection profiles. Nevertheless, actual stress field derived from GPS measurements in the study area does not support the present-day right-lateral kinematics along the Sciacca Fault. Moreover, seismic events show focal mechanisms with the left-lateral component. All these information in a coherent reconstruction show that the reconstructed fault pattern formed under a right-lateral regime; in recent times a change of the slip direction along the Sciacca Fault occurred, due to a change of the direction of principal horizontal stress. Three-dimensional mechanical simulations of the Sciacca Fault system within the Sicilian Channel produce deformation that matches geologic observations and demonstrate the first order impact of fault geometry on uplift patterns and slip potential. Incorporating 3D fault geometry in regional will provide a more accurate understanding of active faulting in the northern part of Sicilian Channel, which is critical for hazard modelling that is used to identify regions most susceptible to earthquake damage. Two boundary-element method models have been tested, to verify subsurface structure interpretation of and slip potential. The results of the first model where both segments of the Sciacca Fault was tested show the difference in the slip potential. The northern segment show limited displacement while the southern segment slip. Similar activity is observed along the Sciacca Fault, where the southern segment, which comprises Nerita and the Eastern side of the Terrible Bank show active sea-floor deformation, however, the northern segment does not show any recent tectonic activity. Also, the seismological data confirm the difference of activity along the Sciacca Fault. The second model, where we intentionally locked the northern segment and let freely slide the southern segment, show fair match between the uplift pattern seen in the model and Sicilian Channel. Scaled sandbox models were used to investigate the 4D evolution (XRCT technique) of transcurrent structure and its interaction with pre-existing thrust belt structure. The analysed tectonic regimes are pure strike-slipe, transpression and transtension. Transpressional models consist of two conjugate faults which dip angle values decrease with the higher amount of obliquity. Pure strike-slip model is built by two conjugate faults and one sub-vertical fault which is positioned above the principal displacement zone (PDZ). The transtensional models present the evolution from primary and splay faults mechanism (lower angle of obliquity) to two highly dipping conjugate oblique-normal faults bounding several minor sub-vertical faults mechanism (higher angle of obliquity). The evolutional model of splay faults which are positioned only on the one side of the primary fault is proposed. Similar structural styles we observe in the transcurrent part of our models were compared to several natural cases.