Seismic Swarm VS20120915.1 in the Canary Islands, Spain

The seismic swarm designated VS20120915.1 occurred in the Canary Islands region of Spain between 19:34 on 14 September 2012 and 21:01 on 17 September 2012. Over 73 hours and 26 minutes, the event sequence comprised 53 earthquakes. Magnitudes ranged from 2.3 to 3.2, with the majority falling between 2.5 and 2.8. Focal depths were predominantly 19–23 km, although one event reached a shallower depth of 10 km. The Canary Islands form a volcanic archipelago situated approximately 100 km off the northwest coast of Africa. Their origin is attributed to hotspot volcanism linked to a mantle plume beneath the African plate. The islands rest on Jurassic oceanic crust and exhibit a west-to-east age progression, with the westernmost islands (El Hierro and La Palma) remaining volcanically active. Tenerife hosts the stratovolcano Teide, while submarine volcanic edifices and rift zones characterize the regional geology. Seismic swarms are a recurrent feature of the archipelago, reflecting both tectonic stresses along fracture zones and magmatic intrusions. Such sequences often occur without immediate surface eruption but can signal subsurface fluid migration or pressure changes within the volcanic system. Depths around 20 km align with the typical brittle-ductile transition zone in this intraplate setting. Since 1 January 2000, seven swarms have been recorded in the region. Earlier activity included five swarms in 2011 and two in 2012, underscoring the episodic nature of unrest. The 2012 swarm examined here fits this pattern, with events clustered tightly in both time and space. Analysis of the temporal distribution shows peak activity on 15 September, when 22 events were registered. Magnitudes remained modest throughout, suggesting limited energy release consistent with fluid-driven rather than large-scale fault rupture. The absence of events exceeding magnitude 3.2 indicates that the sequence did not escalate to levels typically associated with significant volcanic hazard. Ongoing monitoring by Spanish institutions continues to track similar swarms, contributing to improved understanding of Canary Islands volcanism. The data from VS20120915.1 provide a valuable reference for distinguishing background seismic rates from potential precursors. References
SeismoSight internal swarm classification database
Instituto Geográfico Nacional (IGN) seismic catalogue for the Canary Islands
Geological Survey of Spain (IGME) regional volcanic framework reports