Sicily's magnitude 5.5 offshore quake was one of 80 tremors in a single day
The magnitude 5.5 earthquake at 12:19 Italian time on Friday, in the Tyrrhenian Sea near Alicudi, was felt from Palermo to Catania and triggered a tsunami alert that was lifted about an hour later. Counting INGV's catalogue, we found 80 tremors of magnitude 2 or more in that patch of sea on the day, against 9 in the previous seven days.
A magnitude 5.5 earthquake struck the Tyrrhenian Sea off Sicily at 12:19 Italian time on Friday (11:19 in Lisbon). The epicentre was offshore, north-west of the Aeolian Islands near Alicudi, about 9 kilometres down, according to the event record at Italy’s National Institute of Geophysics and Volcanology.
It was felt from Palermo to Catania and across the Aeolian Islands. INGV’s Tsunami Alert Centre issued a warning straight away, as the international protocol requires, and withdrew it roughly an hour later after no change in sea level was detected. Schools and offices were evacuated as a precaution. By the end of the day there were no reports of injuries or damage.
Not a one-off
The 5.5 was the largest shock in a sequence that had been building. A magnitude 4.8 came at 11:51 Italian time. Another, of 5.0, followed at 15:55 and was again felt in Palermo and the Aeolians.
So we counted. In INGV’s public earthquake catalogue we pulled every tremor of magnitude 2 or more in a box of sea around the epicentre (38.6 to 38.95 degrees north, 13.95 to 14.35 east) between 16 and 23 October, in UTC. The previous seven days produced 9. Friday alone, up to the time of our query, produced 80, and 22 of those were magnitude 3 or above.
That jump, more than the 5.5 on its own, is what has Sicily on edge. INGV’s head of earthquakes, Salvatore Stramondo, placed the 12:19 shock within an ongoing sequence of at least 60 tremors over the past week.
What happens next
Nobody can say how a sequence like this ends. It may fade within days or produce another strong shock.
It is not southern Italy’s first scare this year. In August, a magnitude 4.7 quake at the Campi Flegrei was the strongest there in 40 years.
Chart: Tugadaily, from INGV earthquake catalogue data
