Location:

Period:

19 Apr 2021 03:18:57 - 19 Apr 2021 13:31:05 (10 hours 12 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.0; 52 km NW of Santa Cruz, Chile; (11 Mar 2010) (65km from the swarm center)

18 swarms found nearby.

2001

S20011209.2(26.0km)

8 Dec

1 day 23 hours

34 earthquakes

2008

PS20081219.1(164.8km)

18 Dec

1 day 14 hours

8 earthquakes

2010

PS20100227.5(92.2km)

27 Feb

3 days 19 hours

62 earthquakes

PS20100227.1(117.7km)

27 Feb

15 hours

22 earthquakes

PS20100227.4(142.0km)

27 Feb

7 hours

11 earthquakes

PS20100227.7(136.7km)

27 Feb

2 days 14 hours

14 earthquakes

PS20100304.1(32.1km)

3 Mar

1 day 13 hours

7 earthquakes

PS20100305.1(87.1km)

4 Mar

1 day 22 hours

7 earthquakes

PS20100308.1(56.5km)

7 Mar

19 hours

6 earthquakes

PS20100308.2(162.9km)

8 Mar

6 hours

6 earthquakes

PS20100311.1(66.2km)

11 Mar

2 days 16 hours

21 earthquakes

2011

PS20110317.2(165.7km)

16 Mar

16 hours

5 earthquakes

2014

S20140305.2(49.2km)

4 Mar

1 day 2 hours

25 earthquakes

2015

PS20150917.2(191.4km)

17 Sep

21 hours

9 earthquakes

2017

S20170423.1(113.5km)

22 Apr

5 days 22 hours

182 earthquakes

S20170428.1(98.1km)

27 Apr

2 days 11 hours

41 earthquakes

PS20170428.1(91.7km)

28 Apr

2 hours

6 earthquakes

2021

S20210421.1(7.4km)

20 Apr

4 days 0 hours

68 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20210419.1: Analysis of Activity off San Antonio, Chile

A seismic swarm designated PS20210419.1 occurred 81 km west-southwest of San Antonio, Chile, from 03:18 to 13:31 on 19 April 2021. Within 10 hours and 12 minutes, five earthquakes were recorded. The events registered magnitudes between 4.2 and 5.2 at depths ranging from 3 km to 12 km.

The sequence began with a magnitude 5.1 event at 03:18:57 (12 km depth), followed by a magnitude 5.2 at 04:11:26 (8 km depth). Subsequent shocks included a magnitude 5.1 at 11:13:28 (10 km depth), a magnitude 5.0 at 13:05:26 (10 km depth), and a magnitude 4.2 at 13:31:05 (3 km depth). These closely spaced occurrences in both time and location characterize the swarm as a cluster of moderate seismic activity without a single dominant mainshock.

The region lies along the convergent boundary where the Nazca Plate subducts beneath the South American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismicity along the Peru-Chile Trench. The swarm location corresponds to the offshore segment of the subduction zone near the transition between the Maule and Valparaíso segments, areas known for both interplate thrust events and intraslab activity.

Historical records since 2000 indicate 17 prior swarms in the vicinity, distributed across 2001 (1 swarm), 2008 (1), 2010 (9), 2011 (1), 2014 (1), 2015 (1), and 2017 (3). A magnitude 7.0 earthquake on 11 March 2010, located 52 km northwest of Santa Cruz and approximately 65 km from the swarm center, represents one of the stronger events in the broader area during this period. Such swarms are common expressions of stress release in the subduction interface and overlying crust.

The 19 April 2021 swarm reflects ongoing tectonic adjustment in a highly active margin. Depths between 3 km and 12 km suggest involvement of both shallow crustal faults and the upper portion of the subducting slab. No damage or tsunami generation was associated with these moderate-magnitude events.

References

SeismoSight internal swarm classification PS20210419.1
USGS Earthquake Catalog (regional tectonics and historical events)
Global CMT Project (plate boundary parameters)