During 2021, the INGV National Seismic Network recorded an average of 44 earthquakes per day located by the Institute's 24-hour Surveillance Rooms: about 1 every 30 minutes. To find out more, we interviewed Maurizio Pignone, an INGV geologist, who provided us with very interesting data on the seismicity that characterized the year which has just ended.
Maurizio, how many earthquakes were located by the INGV Operations Rooms in 2021?
In 2021 (RSN) has located 16095 earthquakes in Italy and in the surrounding areas. A quantity of events slightly lower than that of 2020 and which has remained stable since 2019, down compared to the years 2016-2017-2018 characterized by the, which began on 24 August 2016. The contribution of this sequence in terms of number of events is still important also in 2021, still representing a very high value compared to the total seismicity in Italy: around 30%.
When and where did the first and last earthquake of the year occur?
The first earthquake of the year occurred . It happened about 1 hour and 3 minutes after the start of the new year! The affected area is seismically rather active, located at the crossroads of several important seismic areas.
The last one however interested and occurred at 23:31 pm on December 31, 2021, less than half an hour before the end of the year. In this case the event was located at the northern end of the area affected by the seismic sequence of Central Italy, which began on 24 August 2016 with the Amatrice earthquake and is still active today.
Where did the strongest seismic events occur?
In 2021, as well as in 2020, the strongest seismic events were located outside the Italian territory. Seismic events of magnitude equal to or greater than 5.0 have in fact occurred in Algeria, Croatia and the Adriatic Sea.
On January 6, an earthquake measuring 5.2 occurred a few kilometers from Petrinja. The event is related to the seismic sequence that started in Croatia at the end of 2020 with the of 29 December.
Furthermore, on March 18, two earthquakes were recorded on the coast of Algeria, respectively of. For the first earthquake, the CAT-INGV issued aTsunami Warning Level Orange (Advisory) for the coasts of Algeria close to the epicenter and an information message for the other coasts of the Mediterranean Sea, including Italy.
Finally, the last days of March were characterized by, started with the occurred about 80 kilometers from the coasts of Puglia Gargano and the Tremiti Islands and about thirty kilometers from the Croatian island of Lastovo.
Were most of the earthquakes that occurred during the year felt by the population?
No, the vast majority of earthquakes located in Italy in 2021 had a magnitude equal to or less than 2.0, and were not felt by the population, with some exceptions in the case of very superficial hypocentres near inhabited areas, such as in volcanic areas of Campania. For this reason, many events were not noticed by the citizens.
What was the region characterized by the highest number of seismic events?
Sicily is confirmed again this year. The region it was in fact characterized by 81 events of magnitude equal to or greater than 2.5. However, if we counted even very small earthquakes, the primacy would be conditioned by the density of the seismic network and Marche and Umbria would "win" with respectively about 3.000 and 5.000 events. Of course, for Sicily the presence of Etna has an impact, where volcanic activity is accompanied by even major earthquakes. In 2021, various areas were also active in the eastern part of the island, in the northern one and in the Aeolian Islands archipelago.
And the one with the fewest earthquakes?
Sardinia! It is the region of Italy furthest from the deformation bands of the Apennines and the Alps, where the great geological processes, which also affected it in an intense geological past not too remote, have slowed down. This does not mean that Sardinia does not have its own relevant seismicity, as described, but it is certainly rarer than in other Italian regions. Also counting the marine areas around the island, in 365 days of 2021 we recorded 7 earthquakes, 5 of which on the mainland (in the province of Nuoro) probably attributable to quarry explosions. The other two took place in the central Tyrrhenian Sea, off Tortolì, along the eastern side of the island. It should also be remembered that the coverage of the National Seismic Network on the island is rather poor, so it is possible that small earthquakes have not been located.
To conclude, what are the tools available to citizens to learn more about the events that characterized 2020?
The 2021 seismicity recorded by the INGV National Seismic Network is shown in an interactive map - dashboardsa
This application shows earthquakes with a magnitude greater than or equal to 1.5, classified and themed according to their magnitude. Each event can be interrogated to view the related hypocentral parameters. Infographics are also available in the application which show, for an area chosen by the user, the total number of earthquakes located in 2021, their maximum magnitude and their distribution over the 12 months of the year.
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