Seismic Swarm S20130322.1 in the Canary Islands: Characteristics and Context

The Canary Islands, an autonomous community of Spain located approximately 100 km off the northwestern coast of Africa, form a volcanic archipelago shaped by hotspot volcanism associated with a mantle plume beneath the African tectonic plate. The islands exhibit a range of ages, with the easternmost being oldest and the westernmost, including El Hierro and La Palma, remaining volcanically active. This geological setting produces frequent seismic activity linked to magma movement, fluid migration, and regional tectonics. Earthquakes in the region typically occur at depths of 10–20 km within the crust, reflecting the interaction between ascending mantle-derived melts and the overlying lithosphere.

Seismic swarms, defined as clusters of earthquakes without a dominant mainshock, are recurrent features of Canary Islands volcanism. They often signal episodes of unrest beneath volcanic edifices. Swarm S20130322.1, recorded in the Canary Islands region, began at 22:59 on 21 March 2013 and concluded at 05:17 on 1 April 2013. Over 246 hours and 18 minutes, 476 earthquakes were detected. This event aligns with a documented pattern of swarm activity since 2000, during which nine such swarms have occurred, including five in 2011, three in 2012, and one in 2013.

Analysis of the initial 100 events reveals a consistent pattern of low-to-moderate magnitude seismicity. Magnitudes ranged from 2.2 to 3.5, with the majority falling between 2.5 and 2.9. Depths clustered tightly between 12 and 18 km, averaging near 15–16 km, consistent with mid-crustal processes beneath the volcanic chain. Early events on 22 March were predominantly 2.5–2.8 in magnitude at 13–18 km depth. By 23 March, several events reached or exceeded 3.0, culminating in a maximum of 3.5 at 14:09 on that day at 15 km depth. Subsequent events maintained similar depth ranges while showing occasional spikes above 3.0, such as 3.4 at 18:00 on 23 March. This progression suggests a gradual buildup of stress release without escalation to higher magnitudes within the first 100 occurrences.

Such swarms contribute to ongoing monitoring efforts by institutions tracking volcanic hazards in the archipelago. The 2013 activity fits within a broader historical framework of intermittent unrest, particularly in the western islands, where magma intrusion episodes have been recorded multiple times in the preceding decade. Depths and magnitudes observed align with typical values for non-eruptive swarms in this setting, where energy release remains diffuse across numerous small events.

References

• Instituto Geográfico Nacional (IGN), Spain: Seismic catalogs for the Canary Islands.
• Geological Survey of Spain (IGME): Volcanic and tectonic framework of the Canary archipelago.
• SeismoSight internal classification records for swarm parameters.