Location:

Period:

28 Apr 2017 15:30:06 - 28 Apr 2017 17:41:49 (2 hours 11 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

20 swarms found nearby.

2001

S20011209.2(77.2km)

8 Dec

1 day 23 hours

34 earthquakes

2003

S20030602.1(35.5km)

2 Jun

3 days 11 hours

65 earthquakes

S20030724.1(93.2km)

23 Jul

2 days 22 hours

48 earthquakes

2007

PS20070329.1(183.8km)

29 Mar

3 hours

6 earthquakes

2008

PS20081219.1(77.7km)

18 Dec

1 day 14 hours

8 earthquakes

2010

PS20100227.5(181.3km)

27 Feb

3 days 19 hours

62 earthquakes

PS20100304.1(61.2km)

3 Mar

1 day 13 hours

7 earthquakes

PS20100305.1(168.7km)

4 Mar

1 day 22 hours

7 earthquakes

PS20100308.1(107.6km)

7 Mar

19 hours

6 earthquakes

PS20100308.2(71.6km)

8 Mar

6 hours

6 earthquakes

PS20100311.1(124.1km)

11 Mar

2 days 16 hours

21 earthquakes

2011

PS20110317.2(75.5km)

16 Mar

16 hours

5 earthquakes

2014

S20140305.2(46.6km)

4 Mar

1 day 2 hours

25 earthquakes

2015

PS20150917.2(112.3km)

17 Sep

21 hours

9 earthquakes

2017

S20170423.1(36.7km)

22 Apr

5 days 22 hours

182 earthquakes

S20170428.1(18.0km)

27 Apr

2 days 11 hours

41 earthquakes

2021

PS20210419.1(91.7km)

19 Apr

10 hours

5 earthquakes

S20210421.1(98.6km)

20 Apr

4 days 0 hours

68 earthquakes

2022

S20220504.1(113.0km)

4 May

1 day 5 hours

42 earthquakes

2026

S20260601.1(53.7km)

31 May

3 days 14 hours

51 earthquakes

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Seismic Swarm Offshore Valparaíso, Chile: April 28, 2017 Event Analysis

The offshore region near Valparaíso, Chile, forms part of the Peru-Chile Trench, where the Nazca Plate subducts beneath the South American Plate at rates of 6–7 cm per year. This convergent margin produces frequent seismic activity, including both large megathrust earthquakes and smaller clustered events known as swarms. On April 28, 2017, a swarm occurred in this zone, lasting 2 hours and 11 minutes and comprising six earthquakes.

The sequence began at 15:30:06 UTC with a magnitude 5.9 event at 22 km depth. Subsequent shocks included a magnitude 5.1 at 15:49:41 (10 km depth), a magnitude 5.4 at 15:58:33 (22 km depth), a magnitude 3.2 at 16:03:28 (24 km depth), a magnitude 5.8 at 16:05:57 (27 km depth), and a final magnitude 5.3 at 17:41:49 (17 km depth). Depths remained shallow to intermediate, consistent with activity along the plate interface and within the overriding crust.

Valparaíso lies within the same tectonic framework responsible for Chile’s major historical earthquakes, such as the 1906 Valparaíso event (estimated magnitude 8.2) and the 1985 Central Chile earthquake (magnitude 8.0). These events released accumulated strain along the subduction zone, which continues to generate both isolated large quakes and episodic swarms. Since 2000, sixteen swarms have been recorded in the broader offshore Valparaíso area, occurring in 2001 (1), 2003 (2), 2007 (1), 2008 (1), 2010 (6), 2011 (1), 2014 (1), 2015 (1), and 2017 (2). The 2010 cluster coincided with aftershock sequences following the Maule earthquake, illustrating how swarms can accompany or follow major strain release.

Such swarms typically reflect fluid migration or localized stress adjustments rather than foreshock sequences leading to a single larger rupture. Monitoring by regional seismic networks helps distinguish these patterns, supporting improved hazard assessment along Chile’s central coast.

References

United States Geological Survey Earthquake Catalog
Chilean National Seismological Center (CSN) annual reports
Global CMT catalog for subduction zone parameters