Past events

The reconstruction of the progression of bradyseism in the Phlegraean Fields has been possible since the early 1800s thanks to observations made on the ruins of the Serapeum, a Roman market dating back to the 1st - 2nd century AD, located a few meters from the port of Pozzuoli. Thanks to the dating of the holes produced by marine mollusks at various heights on the columns of the Serapeo, it was possible to reconstruct the sea level oscillations over the centuries due to the uplift or lowering of the ground. More recently, since 1905, geodetic leveling techniques and, in recent decades, satellite measurements (GPS and interferometry) have made it possible to measure ground movements more accurately and thus to monitor the phenomenon of bradyseism.

Early data from the leveling network show that between 1905 and 1945, the Phlegraean Fields area was affected by continuous subsidence, equal to about 100 cm measured near the "Serapeo," with an average rate of about 2.5 cm/year. Afterward, there was a trend reversal because, between 1945 and 1953, the ground began to rise again by more than 50 cm without significant seismicity. In 1970-72 and 1982-84, two intense bradyseismic crises followed.

The crisis of the '70s. The bradyseismic crisis between 1970 and 1972 was marked by a total uplift (started in 1968) of about 177 cm, with a maximum rate of 6.2 cm/month. In early 1970, numerous cracks were reported in the dry-stone walls that protected the Cumana railway route and some buildings in the historic center of Pozzuoli. Fishermen reported several pieces of evidence that pointed to an uplift of the ground, such as the different inclination of the ferry gangways or the uplift of an arch in the small harbor, under which boatmen could pass for a few months while standing on their boats.

The uplift was accompanied by earthquake swarms with low magnitude, primarily unnoticed by the population. In particular, about 2600 quakes were recorded between February 28 and October 30, 1970, all with low magnitude (M<2.0), focused in the central zone of maximum caldera uplift. On March 3, 1970, the evacuation of the Rione Terra began, as many of the houses showed cracks, and it was feared they could not resist possible stronger seismic quakes. The people displaced from their homes were placed in a hospital and several hotels along the Domitian coast, waiting for the development of the future Rione Toiano. After the crisis, a slow phase of ground lowering to about 21 cm from the maximum uplift began.

Following the events, a particular Law (No. 475 of July 19, 1971) was issued, mandating adherence to the requirements valid for second-category seismic zones for new construction within the municipality of Pozzuoli.

The crisis of the '80s. The following bradyseismic crisis occurred between 1982 and 1984 and reached a maximum uplift of 179 cm, totaling 334 cm since 1970. The maximum uplift rate was 14.5 cm/month. Earthquakes and intense swarms accompanied the uplift: over 16,000 events were recorded during the crisis, with two quakes of M=4.0.

In particular, seismicity became significant in the spring of 1983. From that time on, the buildings of Pozzuoli were under continuous seismic stress with small energy but widespread events and more isolated events of higher energy. A significant increase in seismic activity occurred between September 4 and October 4, 1983, when an earthquake of M=4.0 occurred with an epicenter near the Solfatara and a depth between 2.5 and 3.0 km. The event resulted in damage and panic in the city of Pozzuoli. The earthquake was felt in a radius of more than 30 km. The intensity in the epicentral area (Pozzuoli) was grade VII on the MCS scale, while in parts of Naples, it was grade VI. As a result of the damage to many buildings in Pozzuoli due to the continuous seismic stresses, it was again decided to evacuate part of the population, which, after an initial period spent in the tourist resorts of the Domitian coast, was housed in the new neighborhood of the Monteruscello area. During the last months of 1984, the phenomenon's intensity decreased, and the seismic crisis closed with the December 8 earthquake event of M=3.8.

From 1985, the activity was again characterized by a phase of ground subsidence, which reached a total value of about 94 cm in November 2004. During this period, there were three brief episodes of uplift, in 1989, 1994, and 2000, all less than 10 cm, accompanied by low-magnitude seismic swarms.