The Phlegrean fields beneath the sea: the underwater volcanic district of Naples, Italy

 Following the bradyseimic crises of 1970 and 1984, the Institute of Oceanology of the Istituto Universitario Navale (IUN) of Naples held, all around the Pozzuoli area, high-resolution reflection seismic surveys, occasionally multi-channel but generally single channel. In this paper an interpretation of seismic data is presented, integrated with magnetic information (where available), which aims to better outline the underwater volcanic district. The tectonic features and the main faults which gave origin to the Phlegrean volcanism were identified and the existence of a basement fault zone, 1.5 km wide and more than 6 km long, inside the Pozzuoli Gulf, has been documented. An overall uplift of 500 m of the Pozzuoli shoreline, after the development of the underwater caldera, was also recognised. Fluid traps were depicted and a fluid circulation inside the basement (at more than 4000 m depth) is hypothesised. These may justify the large amount of vapours and gases in the sedimentary column.