Seismic swarm S20210124.2 was recorded in Sicily, Italy, beginning at 03:05 on 24 January 2021 and concluding at 18:23 on 25 January 2021. Over this 39-hour period, 35 earthquakes were detected, with magnitudes ranging from 2.0 to 2.2 and focal depths between 9 and 23 km. The sequence exhibited typical swarm characteristics, featuring closely spaced events without a dominant mainshock, consistent with patterns observed in tectonically active regions.
The events clustered primarily on 24 January, with 32 occurrences distributed across morning and afternoon hours, followed by three additional events on 25 January. Depths remained moderate, suggesting activity within the upper crust. Such swarms often arise from fluid migration or minor stress adjustments along faults rather than large-scale rupture.
Sicily occupies a key position at the convergent boundary between the African and Eurasian plates. This setting drives regional seismicity through a combination of subduction, strike-slip faulting, and extension in the Tyrrhenian Sea back-arc basin. The island's geology includes the Sicilian Fold and Thrust Belt, formed by the collision of the African margin with the European plate since the Miocene. Active structures such as the Malta Escarpment and the Ionian Fault System contribute to frequent low-to-moderate magnitude events.
Mount Etna, Europe's largest active volcano located on Sicily's eastern coast, adds a volcanic component to local seismicity. Although the swarm's location aligns with broader Sicilian tectonics, its timing and depth range overlap with zones influenced by Etna's magmatic system. Historical records show Sicily experiences recurrent seismic swarms linked to both tectonic and volcanic processes.
Since 2000, three prior swarms have been documented in the region: one in 2002, one in 2011, and one in 2018. The 2021 swarm continues this pattern of episodic, low-magnitude clustering. These events underscore Sicily's persistent seismic hazard, where swarms serve as indicators of crustal stress rather than immediate precursors to larger earthquakes.
Monitoring networks operated by Italy's National Institute of Geophysics and Volcanology provide continuous data on such sequences, aiding in refined hazard assessments. The 2021 swarm's parameters remain within expected ranges for background activity in this plate-boundary environment.