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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:
6 km WSW of La Parguera, Puerto Rico
Period:
24 Jun 2021 16:28:21 - 1 Jul 2021 08:01:21 (6 days 15 hours 33 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
127
20 swarms found nearby.
2018
S20181215.1(19.3km)
14 Dec
4 days 6 hours
109 earthquakes
2019
28 Dec
244 days 6 hours
9147 earthquakes
2020
S20200107.1(12.8km)
7 Jan
1 day 21 hours
53 earthquakes
1 May
2 days 18 hours
36 earthquakes
S20201007.2(10.9km)
6 Oct
22 days 9 hours
229 earthquakes
17 Nov
35 days 20 hours
447 earthquakes
23 Dec
46 days 11 hours
2842 earthquakes
2021
S20210108.1(19.2km)
7 Jan
13 days 20 hours
148 earthquakes
29 Jan
2 days 1 hours
29 earthquakes
S20210718.1(21.7km)
17 Jul
3 days 1 hours
37 earthquakes
2022
1 Feb
37 days 20 hours
630 earthquakes
21 Mar
19 days 5 hours
207 earthquakes
23 Apr
17 days 11 hours
189 earthquakes
5 Aug
13 days 6 hours
262 earthquakes
2023
14 Mar
6 days 9 hours
92 earthquakes
8 Apr
10 days 15 hours
189 earthquakes
30 Sep
3 days 22 hours
63 earthquakes
23 Oct
1 day 13 hours
25 earthquakes
2025
12 Mar
4 days 6 hours
74 earthquakes
20 Mar
5 days 23 hours
70 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20210625.1: Analysis of Activity Near La Parguera, Puerto Rico

Puerto Rico occupies a tectonically active zone at the boundary between the Caribbean and North American plates. The island experiences frequent seismicity driven by oblique subduction along the Puerto Rico Trench to the north and left-lateral strike-slip motion along the Enriquillo-Plantain Garden fault zone to the south. Southwestern Puerto Rico, including the area around La Parguera, lies within the Western Puerto Rico Deformation Belt, where shallow crustal faults accommodate regional strain. Earthquakes in this sector commonly occur at depths of 5–15 km within the overriding plate.

Seismic swarms have occurred periodically in the region. Since 2000, nine swarms have been documented, with one in 2018, one in 2019, five in 2020, and two in 2021. These episodes typically feature clustered events of moderate magnitude without a single dominant mainshock, consistent with fluid migration or slow slip on local fault networks.

Swarm S20210625.1 began at 16:28 UTC on 24 June 2021 and concluded at 08:01 UTC on 1 July 2021, lasting 159 hours and 33 minutes. The epicentral area was located 6 km west-southwest of La Parguera. During this interval, 127 earthquakes were recorded. The first 100 events exhibited magnitudes ranging from 0.9 to 4.3, with the majority falling between 2.0 and 3.5. Depths remained shallow, concentrated between 9 and 12 km, indicating activity within the upper crust. The largest event reached magnitude 4.3 at 20:10 UTC on 24 June at 11 km depth. Subsequent activity showed a gradual decline in both rate and maximum magnitude, with events after 27 June rarely exceeding magnitude 3.2.

Temporal distribution revealed two phases of elevated productivity on 24–25 June and 27 June, separated by quieter intervals. Most events clustered tightly in space and time, a hallmark of swarm behavior rather than a classic foreshock–mainshock–aftershock sequence. The absence of events deeper than 12 km suggests limited involvement of the subducting slab interface.

This swarm fits the established pattern of shallow seismicity in southwestern Puerto Rico. Comparable episodes in 2020 were linked to reactivation of local normal and strike-slip faults under regional transpression. Continued monitoring remains essential given the proximity to populated coastal communities and the historical occurrence of damaging earthquakes in the region, such as the 1918 Mw 7.1 event and the 2020 Mw 6.4 mainshock.

References

USGS Earthquake Catalog
Puerto Rico Seismic Network historical reports
Caribbean tectonic framework summaries from the Incorporated Research Institutions for Seismology (IRIS)