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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
STRAIT OF GIBRALTAR
Period:
6 Jun 2021 07:44:55 - 17 Jun 2021 09:18:03 (11 days 1 hour 33 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
144
16 swarms found nearby.
2016
PS20160125.1(13.6km)
25 Jan
1 hours
6 earthquakes
2021
15 May
3 days 23 hours
51 earthquakes
S20210730.3(18.8km)
29 Jul
57 days 9 hours
1361 earthquakes
13 Nov
5 days 5 hours
78 earthquakes
20 Nov
5 days 9 hours
57 earthquakes
5 Dec
5 days 18 hours
57 earthquakes
20 Dec
10 days 0 hours
135 earthquakes
2022
5 Feb
8 days 15 hours
147 earthquakes
7 Apr
28 days 16 hours
392 earthquakes
S20220520.1(10.3km)
19 May
21 days 19 hours
412 earthquakes
16 Jun
6 days 9 hours
74 earthquakes
19 Jul
22 days 3 hours
330 earthquakes
15 Sep
4 days 1 hours
55 earthquakes
3 Oct
5 days 4 hours
91 earthquakes
S20221016.1(15.8km)
15 Oct
5 days 23 hours
62 earthquakes
2024
15 Mar
2 days 2 hours
32 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm Activity in the Strait of Gibraltar: June 2021

The Strait of Gibraltar region experienced a notable earthquake swarm designated S20210607.1. Activity commenced at 07:44 on 6 June 2021 and concluded at 09:18 on 17 June 2021, spanning 265 hours and 33 minutes. During this period, 144 earthquakes were recorded within the strait, which forms the narrow marine passage separating the Iberian Peninsula from northwest Africa.

Analysis of the first 100 events reveals a sequence dominated by low-magnitude tremors. Magnitudes ranged primarily between 1.6 and 3.0, with the majority falling below 2.5. Depths varied from shallow levels near 1 km to intermediate depths reaching 51 km, indicating a mix of crustal and slightly deeper sources. Early events on 6 June included magnitudes of 1.8 at 5 km depth and 2.8 at 11 km, followed by a gradual increase in frequency and occasional peaks such as a 3.0 magnitude event at 3 km on 7 June. Subsequent days showed sustained activity with clusters around 10–20 km depth, interspersed with deeper occurrences up to 48–51 km by 9 June. This pattern reflects typical swarm behavior without a single dominant mainshock.

The Strait of Gibraltar lies at the convergent boundary between the Eurasian and African tectonic plates. The African plate moves northward at approximately 4–5 mm per year relative to Eurasia, producing a transpressive regime with strike-slip and reverse faulting. This setting generates moderate seismicity across the Gibraltar Arc, encompassing the Betic Cordillera in southern Spain and the Rif Mountains in Morocco. The region forms part of the broader Western Mediterranean tectonic framework, influenced by the ongoing closure of the Tethys Ocean remnants.

Historical records indicate limited swarm occurrences since 2000, with only two documented events prior to 2021. A single swarm took place in 2016, followed by the 2021 episode. Regional seismicity has featured occasional moderate earthquakes, though swarms remain infrequent compared to more active segments of the plate boundary farther east.

This swarm provides insight into localized stress release along secondary faults within the strait. Event depths suggest activation across multiple structural levels, consistent with the complex fault network in the area. Continued monitoring supports improved understanding of seismic hazards at this strategic tectonic junction.

References:
SeismoSight internal classification data for swarm S20210607.1
USGS Earthquake Hazards Program regional tectonic summaries
EMSC Mediterranean seismicity reports (updated 2023)