Seismic Swarm VS20201224.1 in the Canary Islands Region

The Canary Islands, an archipelago situated approximately 100 km off the northwest coast of Africa, represent a classic example of intraplate oceanic volcanism driven by the Canary hotspot. This mantle plume has generated the seven main islands over millions of years through successive phases of shield-building and erosional activity. The region exhibits a well-documented history of volcanic and seismic events, with eruptions recorded on La Palma in 1971 and 2021, as well as earlier activity on Tenerife and El Hierro. Seismic swarms frequently accompany magmatic intrusions at depths of 10–35 km, reflecting the islands’ active geodynamic setting within the African plate.

SeismoSight recorded swarm VS20201224.1 from 21:26 on 23 December 2020 to 21:29 on 24 December 2020. During this 24-hour period, 65 earthquakes occurred, with magnitudes ranging from 1.5 to 2.3 and focal depths predominantly between 10 km and 35 km. The sequence displayed typical swarm characteristics: a rapid onset, sustained low-to-moderate energy release, and no single dominant mainshock. Early events clustered around magnitudes 1.6–2.2 at mid-crustal depths near 28–30 km, while later activity included shallower events at 1–17 km, indicating possible upward migration of fluids or magma.

Event timing showed highest frequency in the first six hours, with 22 earthquakes registered before midnight on 23 December. Magnitudes remained modest throughout, never exceeding 2.3, consistent with background unrest rather than a major tectonic episode. Depth distribution revealed a primary concentration at 24–32 km, aligning with known magma storage zones beneath the western islands. The absence of felt reports or surface deformation aligns with the small energy release of this particular swarm.

Geological context underscores the swarm’s significance within the Canary volcanic province. The islands sit atop thinned oceanic crust influenced by hotspot upwelling, producing alkaline basaltic magmas. Historical records and modern monitoring by Spain’s Instituto Geográfico Nacional confirm that similar swarms often precede or accompany eruptive phases, although most remain aseismic at the surface. Updated monitoring data through 2023 continue to show recurrent microseismicity in the same depth range, reinforcing the long-term activity of the hotspot system.

Analysis of the 65 events indicates an average magnitude of approximately 1.9 and a mean depth of 26 km. The temporal decay followed a gradual pattern without aftershock-style clustering, supporting a fluid-driven mechanism rather than brittle fault rupture. Such patterns are characteristic of Canary Islands unrest and provide valuable constraints for volcanic hazard assessment.

References

• Instituto Geográfico Nacional (IGN), Spain – seismic catalog and volcanic monitoring reports
• SeismoSight internal swarm classification VS20201224.1
• Geological Society of America – Canary Islands hotspot literature (updated syntheses to 2023)