Seismic swarm S20221002.1 was recorded across Spain from 23:27 on 1 October 2022 to 19:52 on 7 October 2022. The sequence lasted 140 hours and 25 minutes and included 140 earthquakes. Analysis of the first 100 events reveals a typical swarm pattern characterized by low-to-moderate magnitudes and shallow focal depths.
Magnitudes ranged from 1.5 to 3.6, with the largest event (magnitude 3.6 at 2 km depth) occurring early on 2 October at 05:44. Depths clustered between 2 km and 18 km, although isolated events reached 30 km. The majority of events fell between 7 km and 14 km, indicating activity within the upper crust. Temporal distribution showed the highest frequency during the first 48 hours, followed by a gradual decline, consistent with fluid-driven or stress-transfer mechanisms rather than a single mainshock-aftershock sequence.
Geologically, Spain lies at the convergent boundary between the African and Eurasian plates. The southern Iberian Peninsula, particularly the Betic Cordillera, accommodates most regional deformation through a network of strike-slip and thrust faults. This tectonic setting produces moderate seismicity, with occasional earthquake swarms linked to fluid migration along fault zones or minor magmatic processes. Depths observed in S20221002.1 align with the brittle-ductile transition zone documented across the Betics.
Historical records maintained by Spain’s Instituto Geográfico Nacional indicate only two swarms have occurred nationwide since 1 January 2000. The first took place in 2011; S20221002.1 represents the second. Both sequences share similar magnitude ranges and shallow depths, suggesting recurring localized stress conditions within the same broad tectonic domain.
The 2022 swarm did not produce reported damage or felt intensities above IV on the EMS-98 scale, reflecting the modest energy release. Continued monitoring remains essential because swarm activity can precede larger tectonic events in the Betic region.
References SeismoSight internal classification data for swarm S20221002.1 Instituto Geográfico Nacional (IGN) seismic catalogue Geological Survey of Spain (IGME) tectonic framework reports