Active deformation and volcanism offshore Campi Flegrei, Italy: new data from high-resolution seismic reflection profiles

Abstract

The interpretation of high-resolution seismic reflection profiles permitted the identification of many geologic features in the inner shelf of Pozzuoli Bay. This area corresponds to the offshore of Campi Flegrei: a classically active volcanic area that experienced earthquakes and meter-scale vertical ground uplift before the 1538 Monte Nuovo eruption and in the period from 1970 to 1985. The detected undersea features include two small debris flows that are located in a submarine valley in the western part of Pozzuoli Bay. They may be the result of a pyroclastic flow and a pyroclastic surge that entered the sea. The younger debris flow in the uppermost marine deposits of Pozzuoli Bay formed during the 1538 Monte Nuovo eruption, and the older debris flow during the 3.8 ka-old Averno eruption. Other features detected by our survey are an undersea 8 m-high and 1 km-wide cryptodome, corresponding to a near-surface intrusion, located off Pozzuoli, that warped post-4 ka marine deposits. The interpretation of the cryptodome is based on seismic facies analysis, deformation geometry and correspondence to a magnetic high. It is suggested that this undersea dome formed during the uplift phases associated with the 1538 Monte Nuovo eruption and the two more recent bradyseismic crises of 1970–1972 and 1982–1984. Surface-breaking faults (with maximum vertical offset of 1 m) were recognized in very shallow waters near the coast of Pozzuoli. It is suggested that some of these faults were active during the 1982–1984 bradyseismic earthquake sequence.