Potential tsunami hazard in the central Adriatic and southern Sicilian coasts associated with offshore activities

n recent years, increasing attention has been given to evaluating potential hazards in areas of interest for offshore activities, such as potentially triggered seismicity offshore and its cascading effects, including possibly triggered landslides and tsunamis. In the present work, carried out under the SPIN project ("Test delle Buone Pratiche per lo studio della potenziale interazione tra attività offshore e pericolosità naturali" – “Testing good practices for the study of the potential interaction between offshore activities and natural hazards”), funded by the Italian Ministery for the Environment and the Energetic Security, we present a methodology to model earthquake generated tsunamis and we apply it to two study areas: “Alto Adriatico”, on the Italian central-northern Adriatic coast (southern Emilia-Romagna, Marche and northern Abruzzo regions), and “Canale di Sicilia”, on the southern coast of Sicily around the Gulf of Gela.

The first step of the workflow consists in combining multichannel 2D and high-quality 3D seismic data, morpho-bathymetric data, instrumental seismicity records, and well data to characterize both shallow and deep tectonic features as well as active faults. Then, 3D geological and velocity models at crustal scale are built, in order to simulate the ground shaking with the identified faults with different methods, such as ShakeMap and 3D broadband ground motion simulations.

The identified faults are also considered as potential tsunamigenic sources. The tsunami generation is modelled as an initial condition problem, where the initial water displacement is determined by the coseismic displacement of the seafloor generated by a fault rupture. For a given event, we determine the magnitude of the generated earthquake from scaling laws, assuming the entire fault ruptures. Different possible slip distributions are considered. The propagation of the tsunami is computed under the shallow water approximation on a system of rectangular nested grids. Increased spatial resolution is used in areas of interest, such as harbours and industrial complexes.

In the “Alto Adriatico” area, we consider thrusting faults with magnitudes up to 6.5. However, due to the very shallow bathymetry, the tsunami simulations show modest maximum amplitudes and limited inundation andwatercourses seem not to be affected. Late sea level oscillations are observed in the Ancona harbour. In the “Canale di Sicilia” area, we consider faults with a normal mechanism, with magnitudes up to 6,0. Maximum amplitudes, while still modest, are more sensitive to changes in the location of the maximum slip portion of the fault.