During the last years it has been observed a substantial increase in security request for the areas hosting energy production facilities, especially after the accident occurred in 2010 in the Gulf of Mexico. In this context, since 2014 the Italian government throughout the mineral and energy resources office of the Minister of economic development is facing this challenging task via an operative project aimed at improving the security of the off-shore oil and gas production plants. This project is based on a multidisciplinary approach which points to understand all the security planning aspects around the extraction facilities, involving partners as universities, research centers and consortiums, public companies, as well the Italian Navy. Among them, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) participates in the project dealing with scientific aspects related to seismology, tectonophysics and seismotectonic.

The task of the project entrusted to INGV contains the feasibility studies to improve the security level of the off-shore plants referring to the seismic hazard assessment, as part of an entire security plan.

In this work we present the preliminary results obtained by the design of an innovative useful tool, named CSO (Catalogo della Sismicità Off-shore, Italian Catalogue of Italian Off-shore Seismicity). The idea of this catalogue has grown up since there is a compelling need, not only for the scientific community, to obtain high-quality locations of the seismicity occurred in the Italian off-shore areas to be correctly addressed to active off-shore tectonic structures. This is much more relevant since it allows and constrain further detailed operations regarding the management of security levels of such infrastructures present in seismic areas, as recommended by the aims of the project for oil and gas facilities.

As well known, the solution of an earthquake location problem has a quality decreasing as the earthquake occur outside of the seismic network (azimuthal gap > 180°). The main goal of the CSO is to improve the location quality of the earthquakes occurred in the off-shore domains, reducing uncertainties in location errors. Different tests were produced as a trial-and-error approach, tuning the setting parameters of the location code in order to minimize errors and enhance the accuracy. These preliminary results were obtained using a 1-D average velocity model for the entire dataset, that consistently improved the previous available seismic datasets. The next step to determine a further improve will be to define several "ad hoc" regional velocity models that will much more enhance the quality of locations.

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