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with the contribution of data from broad-band ocean bottom seismometers and hydrophones (OBS/H). Offshore
data were recorded during the TYrrhenian Deep sea Experiment (TYDE) from December 2000 to May
2001 in the Southern Tyrrhenian Sea. Hypocenter locations of a cluster of 53 seismic events occurred in
March 2001 in north-eastern Sicily were estimated by the integration of land (permanent network) and offshore
(temporary network) data and compared with locations estimated from land data only. The scatter of
the cluster was evaluated by dispersion parameters. The off-shore data significantly reduced the scatter of
the swarm hypocenters also restricting the depth range of the cluster. Moreover, space trends of the event
distribution originally shown by the land data were only partially confirmed by the land-sea joint data.
In order to assess the efficiency in terms of hypocenter mislocations in the subject area, of a land-sea
integrated network with respect to a land-based network, we performed simulations by assuming a grid
distribution of earthquakes and a recent local 3D velocity model, computing synthetic arrival times of body
waves to the stations of both network configurations (integrated and land-based) perturbing the computed
times and relocating earthquakes by inversion. The results of the synthetic tests demonstrated that the
presence of sea bottom stations in the Tyrrhenian basin can reduce the mislocations of large magnitude
and/or superficial earthquakes in the southernmost Calabria and Messina Strait and of low magnitude and/or
deep earthquakes in north-eastern Sicily. The major accuracy of synthetic earthquake locations obtained
including OBS/H data provides an additional support to the interpretation of the cluster occurred in March
2001 and to the opportunity of long-term installation of an off-shore network like TYDE in the study region.
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