Rain and seismic tremor in the Phlegraean Fields.

A study, authored by Federiciani professors Nicola Scafetta and Adriano Mazzarella (former professor of Meteorology and retired as of 2019), on the influence of rain on the occurrence of seismic tremors in the Phlegraean Fields, which is causing much alarm to the residents of Pozzuoli these days, has been published in the international journal Water in January 2021 .The area around Solfatara is made highly unstable due to its well-known bradyseism.

The two professors compared from 2008 to 2020 the catalog of earthquakes measured at the Phlegraean Fields with a physical-statistical model derived from the daily rainfall record measured at the University of Naples Meteorological Observatory. The model simulates the time scale of water percolation in the volcanic soil of the Phlegraean Fields according to Darcy's law. A link between rainfall and seismic swarms was thus observed.

The correlation is most evident when the annual number of seismic events is between 50 and 250, as happened from 2008 to 2014. However, a strong association between rainfall events and seismic activity could also be detected in 2018 and 2019 with 375 and 592 tremors, respectively. Even in 2020 (766 earthquake events), the observed high seismic frequency seems to be correlated with the abundant rainfall during this period especially from September until now.

Ultimately, at the Phlegraean Fields large amounts of rain and continuous periods of precipitation are capable of triggering seismic swarms with magnitude up to 3 after a few days and up to two weeks.

The result suggests that rainwater penetrates deep into the hot and highly fractured subsurface of the Phlegraean Fields and, mixing with hydrothermal fluids of magmatic origin that migrate to the surface with temperatures far above 100 °C, cause micro-explosions in the subsurface. These induce seismic swarms in the saturated state, which is localized in the first 2.5 km depth. The effect of meteoric waters is thus combined with bradyseismic effects.

The research proves that the intuitions of Abbot Giovanni Maria della Torre (1710-1782) that the volcanic seismic tremor at the Phlegraean Fields and Vesuvius could also be fostered by rain falling in the crater area were correct. The King of Naples himself, Ferdinand II of Bourbon the established the Vesuvius Observatory in 1841 as a meteorological observatory to study the link between meteorological and volcanic phenomena.

The study proved to be fundamental for a better understanding of earthquakes in the Phlegraean Fields and the development of effective seismic risk protection policies for the city of Pozzuoli and its surroundings.

Scafetta, N.; Mazzarella, A.: 2021. "On the Rainfall Triggering of Phlegraean Fields Volcanic Tremors" Water 13, no. 2: 154. https://www. mdpi.com/2073-4441/13/2/154