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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:
15 May 2021 04:29:55 - 19 May 2021 03:32:30 (3 days 23 hours 2 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
51
16 swarms found nearby.
2016
PS20160125.1(20.7km)
25 Jan
1 hours
6 earthquakes
2021
6 Jun
11 days 1 hours
144 earthquakes
S20210730.3(23.2km)
29 Jul
57 days 9 hours
1361 earthquakes
S20211114.1(14.6km)
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
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
15 Oct
5 days 23 hours
62 earthquakes
2024
S20240316.1(11.6km)
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 in the Strait of Gibraltar: May 2021

The Strait of Gibraltar marks the narrow marine passage connecting the Atlantic Ocean and the Mediterranean Sea, situated between the southern Iberian Peninsula and northern Morocco. This region forms part of the Gibraltar Arc, a tectonically complex zone resulting from the ongoing oblique convergence between the African and Eurasian plates at rates of approximately 4–5 mm per year. The arc encompasses the Betic-Rif mountain belts and the Alboran Sea basin, where a combination of subduction remnants, strike-slip faulting, and crustal extension drives moderate seismic activity.

Seismic swarms in this setting often arise from fluid migration along fault networks or localized stress adjustments rather than large mainshock-aftershock sequences. The area has experienced historical earthquakes, including the 1755 Lisbon event whose effects extended into the strait, underscoring its long-term seismic hazard potential.

On 15 May 2021 at 04:29 UTC, a seismic swarm designated S20210516.1 began in the Strait of Gibraltar. The sequence concluded on 19 May 2021 at 03:32 UTC, spanning 95 hours and 2 minutes. During this interval, 51 earthquakes were recorded. Magnitudes ranged from 1.7 to 3.6, with the largest event occurring on 15 May at 17:20:26 UTC. Focal depths varied between 0 km and 30 km, indicating activity across both shallow crustal levels and slightly deeper structures.

Event timing showed clustering on 15 and 16 May, followed by a gradual decline. Multiple events exceeded magnitude 2.0, including several between 2.4 and 2.9, while the majority remained below 2.0. Depths frequently clustered around 10–20 km, though shallower (0–5 km) and deeper (up to 30 km) occurrences were also documented. This distribution suggests activation along vertically extensive fault segments within the transpressive regime of the strait.

Historical records maintained by SeismoSight indicate that only one prior swarm has been identified in the region since 1 January 2000. That earlier episode occurred in 2016, highlighting the infrequent nature of swarm-type activity compared with isolated tectonic events.

The 2021 swarm provides insight into the low-to-moderate energy release typical of the Gibraltar Strait. No events reached destructive thresholds, yet the sequence illustrates the persistent microseismicity that characterizes this plate-boundary segment. Continued monitoring remains essential for refining seismic hazard models in a region traversed by critical maritime and energy infrastructure.

References

  • SeismoSight internal classification data for swarm S20210516.1
  • Geological background drawn from standard references on the Gibraltar Arc and Betic-Rif domain (e.g., open-access summaries from the Instituto Geográfico Nacional and analogous European geological surveys)