Seismic Swarm VS20210131.1: Canary Islands, Spain Region

A seismic swarm designated VS20210131.1 was recorded in the Canary Islands, Spain region, commencing at 08:54 on 31 January 2021 and concluding at 03:47 on 1 February 2021. Over a period of 18 hours and 52 minutes, a total of 45 earthquakes were registered. Magnitudes ranged from 1.5 to 2.5, with focal depths primarily between 10 and 28 km, though several shallower events occurred at depths as low as 6 km. The sequence exhibited a clustered temporal distribution, with peak activity during the afternoon and evening of 31 January.

The events reflect typical characteristics of volcanic swarm activity in the region. Most earthquakes clustered around magnitudes 1.8–2.2 and depths of 19–24 km, consistent with fluid migration or magmatic processes at mid-crustal levels beneath the archipelago. Shallower events, such as those at 6 km and 10 km, may indicate localized stress adjustments nearer the surface. No single dominant mainshock was observed, confirming the swarm classification rather than a classic foreshock-aftershock sequence.

The Canary Islands form a volcanic archipelago situated on the African tectonic plate, generated by a mantle hotspot that has produced shield volcanoes over millions of years. The islands exhibit ongoing volcanic and seismic activity driven by this intraplate setting, with historical eruptions documented on multiple islands including Tenerife, La Palma, and El Hierro. Seismic swarms frequently precede or accompany magmatic intrusions, serving as key indicators for monitoring potential eruptive unrest.

According to internal classification records, only one swarm has been documented since 1 January 2000, with the preceding event occurring in 2020. This rarity underscores the episodic nature of such sequences within the broader tectonic framework of the region. The 2021 swarm aligns with patterns observed in other hotspot-related volcanic provinces, where low-to-moderate magnitude events signal subsurface movement without immediate surface rupture.

Data from the swarm provide valuable insight into regional seismicity. The consistent depth range suggests activity concentrated along established volcanic conduits rather than shallow tectonic faults. Such monitoring supports hazard assessment for the densely populated islands, where even modest swarms warrant attention due to their potential link to future volcanic episodes.

References

SeismoSight internal swarm classification records VS20210131.1.
Geological Survey of Spain (IGME) regional volcanic framework reports.
Instituto Geográfico Nacional (IGN) seismic monitoring summaries for the Canary Islands.