Location:

Period:

8 Sep 2007 16:43:56 - 10 Sep 2007 21:35:14 (2 days 4 hours 51 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

2 swarms found nearby.

2016

PS20160125.1(47.3km)

25 Jan

1 hours

6 earthquakes

2021

S20210730.3(28.9km)

29 Jul

57 days 9 hours

1361 earthquakes

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Seismic Swarm in the Strait of Gibraltar: September 2007

A notable seismic swarm, designated S20070909.1, occurred in the Strait of Gibraltar between 16:43 on 8 September 2007 and 21:35 on 10 September 2007. In just over 52 hours, 35 earthquakes were recorded, providing insight into the ongoing tectonic dynamics of this narrow waterway separating Europe and Africa.

The events clustered tightly in both space and time, with magnitudes ranging from 1.1 to 2.9. The largest shocks reached 2.9 on 9 September at 07:53 and 2.8 on both 8 September at 16:43 and 10 September at 04:27. Depths remained predominantly shallow, mostly between 0 and 5 km, although several events occurred at 10–15 km. Activity began with a 2.8 magnitude event near the surface, followed by a rapid succession of smaller tremors throughout the evening of 8 September. The swarm intensified again on 9 September, featuring multiple events above magnitude 2.0, including a pair of 2.7 shocks within minutes of each other. By 10 September, activity tapered off, concluding with a final 1.4 magnitude event at 21:35.

This swarm exemplifies the diffuse seismicity characteristic of the Strait of Gibraltar region. The area lies at the westernmost segment of the convergent boundary between the Eurasian and African plates, where slow northwestward motion of Africa produces compressional and strike-slip deformation. The Gibraltar Arc, encompassing the Betic-Rif mountain belts, accommodates this convergence through a combination of thrusting and lateral faulting. Historical records document recurrent moderate earthquakes, while instrumental data confirm persistent low-to-moderate activity linked to the broader Ibero-Maghrebian seismogenic zone.

Geological studies attribute the region’s seismicity to inherited structures from the Alpine orogeny interacting with present-day plate motion. The 2007 swarm, with its lack of a single dominant mainshock and gradual decay of event rate, aligns with patterns observed in other plate-boundary transition zones. Depths mostly under 15 km indicate brittle failure within the upper crust, consistent with the tectonic regime.

SeismoSight internal classification identifies the sequence as a classic swarm without foreshock-mainshock-aftershock progression. Such episodes contribute to long-term strain release along the plate interface and help refine models of seismic hazard for nearby coastal populations in southern Spain and northern Morocco.

References

SeismoSight internal swarm catalog S20070909.1
Geological Survey of Spain (IGME) tectonic framework reports
Moroccan National Seismic Network regional bulletins
European-Mediterranean Seismological Centre (EMSC) historical database