Historic Unrest of the Campi Flegrei Caldera, Italy

Abstract

After some centuries of subsidence, following the AD 1538 Monte Nuovo last eruption, the Campi Flegrei caldera has shown unrest episodes since at least 1950. The first uplift episode dates back to 1950–1952 and amounted to 73 cm, without any report or record of seismic activity. Two strong infla- tion episodes occurred in 1970–1972 and 1982–1984. The first accompanied by moder- ate low seismicity, with only few events felt by the population, whereas the second was accompanied by relatively intense swarms of volcano-tectonic earthquakes, reaching up to magnitude 4. The seismic activity caused alarm in the population and a spontaneous nightly evacuation of part of the town of Pozzuoli (44,000 inhabitants). Since this last episode, subsidence has been recorded for several years, interrupted by some mini-uplift events, lasting several weeks and accompa- nied by seismic swarms of low-magnitude volcano-tectonic events. In recent years, high sensitivity instruments have been installed to detect slow earthquake transients and other mechanical/temperature low-intensity precur- sory signals. Since late 2004 another moderate uplift is occurring at very small rate, amount- ing to about 1–2 cm/year, accompanied by long-period events. This uplift is different from the past mini-uplift events due to its duration. This work summarises all seismic and ground deformation data as well as the models proposed to interpret these phenom- ena, suggesting possible methods for detecting precursors of future eruptive activity in the area.