Active tectonics, sedimentation history and geomorphological features in the northern Sicily continental margin: implications for the marine geohazard assessment

Starting from the assumption that seismic events in the active margins are accompanied by evidence of a depositional, geomorphologic and structural type, which constitutes the geological record of their activity, we analysed different features of the Northern Sicily continental margin (NSCM) to reconstruct the deformational field and related stress field in the Southern Tyrrhenian sea. As an outcome of this project we were going to obtain seismotectonic setting and mapping to provide a powerful tool in managing and assessing the marine geological hazards. The study area extends from the San Vito Peninsula to the Termini Gulf along the NSCM, including the Ustica island, and is located in a transitional area between the Sicilian-Maghrebian chain (SMC) to the south and the Tyrrhenian back-arc basin (TBAB) to the north. We mapped different features (tectonic, geomorphological, depositional, geophysical) in order to collect in a seismotectonic map driving forces and triggering factors, as well as their products along the NSCM. In order to reconstruct the Recent evolution of the study area we analyzed the whole Plio-Quaternary time interval (defining the interval of neotectonics), with emphasis to the Late Pleistocene-Holocene (which define the interval of active tectonics). Products of the tectonic activity are pockmarks, mud volcanoes, structural escarpment, and other seismic induced features (submarine landslides, chaotic deposits, megafloods, channels and canyons and related sedimentary processes). As a second step of this study we investigated geometry, age and kinematics of the tectonic structures, both buried and outcropping (at the seafloor or in the field), and correlate them to the sedimentary evolution of the Plio-Quaternary succession. With the aim to verify whether and where the recently active structures can give rise to tsunamis through the bottom shift associated with slope failures, as the submarine landslides, we implemented a method to assess quantitatively the characteristics of anomalous waves and related coastal run-ups. In detail, following the main aims of the research project, we obtained some major achievements: Timing and kinematic characters of the neotectonic features. Based on the analysis of recent and active faults, seismicity and geodetic data, we reconstructed the present deformational pattern in the NSCM. We analysed the present processes along the Africa Europa boundary, giving new contribution on the characterization of crustal features produced by a change in the polarity of deformation and related seismotectonic setting. Fault systems pattern. We mapped in great detail outcropping and shallow buried faults and fold axes and related morphological features. We found that these structures are in agreement with the present stress field as derived from the focal mechanisms in the study region. The resulting data were used to compile the marine geomorphological and structural layers of the Sheet 585 “Mondello” (Geological Map of Italy on 1:50,000, CARG Project). Submarine morphology, stratigraphy and structures of the Ustica volcanic complex. We analyzed the complex features of the Ustica volcanic edifice and contributed to the knowledge of the geological-geodynamic processes acting in the northern sector of the study region, which occurs on the Africa-Europe plate boundary, just along the thrust front separating the Kabilian-Calabrian tectonic element from the Sicilian-Maghrebian domain. Late Quaternary Tectonics vs Sedimentation history. We investigate the tectonically active NSCM, with a focus on the Termini basin (central Southern Tyrrhenian Sea). This region originated as a consequence of a complex interaction of compressional events, crustal thinning, and strike-slip faulting, which the prevailing control on the morphology of the present day shelf and coastal areas during the Pleistocene. We focused on those related to gravitational mass movement and fluids escape, and dated the seismic-induced landslides in relation to the Late Quaternary depositional sequence. In this way we tentatively calculated the recurrence times of the main earthquakes. Seabed sedimentary structures and bottom currents. We studied for the first time the bottom sedimentary structures along a gully system in a selected area of the NSCM (the Capo Zafferano offshore), to understand the interactions between the depositional processes and the complex morphology of the coastal-offshore areas. We identified bedforms, known as cyclic steps, which are linked to the dynamics of the bottom currents along the canyons. The results point out that turbidity currents might have been few meters thick and have had velocities in the range of 0.2–1.5 m/s. Seismotectonic Map. Starting from the analysis of the processes active in the NSCM we realized the seismotectonic map of this region. The results, managed with a GIS-database, are potential indicators of geohazard for human settlements and infrastructures in the offshore and coastal zones. Tsunami risk generated by submarine landslides. To provide an assessment of the geological hazards including tsunamigenic potential in coastal areas that could be subject to erosion, flooding and seismic activity, we tested some main submarine landslides as potential tsunamigenic source, in two selected sectors of the NSCM, the Gulf of Palermo and the Patti offshore. We calculated the associated theoretical run-ups, and are going to produce simulation models of the propagation of anomalous waves, coastal run-ups and inundation.