Location:

Period:

27 Apr 2017 21:17:32 - 30 Apr 2017 08:47:17 (2 days 11 hours 29 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

9 swarms found nearby.

2003

S20030602.1(20.3km)

2 Jun

3 days 11 hours

65 earthquakes

2008

PS20081219.1(66.9km)

18 Dec

1 day 14 hours

8 earthquakes

2010

PS20100304.1(70.2km)

3 Mar

1 day 13 hours

7 earthquakes

PS20100308.2(66.6km)

8 Mar

6 hours

6 earthquakes

2011

PS20110317.2(67.9km)

16 Mar

16 hours

5 earthquakes

2015

PS20150917.2(97.8km)

17 Sep

21 hours

9 earthquakes

2017

S20170423.1(19.5km)

22 Apr

5 days 22 hours

182 earthquakes

PS20170428.1(18.0km)

28 Apr

2 hours

6 earthquakes

2021

PS20210419.1(98.1km)

19 Apr

10 hours

5 earthquakes

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Earthquake Swarm Offshore Valparaíso, Chile: April 2017 Analysis

An earthquake swarm designated S20170428.1 occurred offshore Valparaíso, Chile, from 21:17 UTC on 27 April 2017 to 08:47 UTC on 30 April 2017. The sequence lasted 59 hours and 29 minutes and included 41 events. This activity unfolded within the seismically active Peru-Chile Trench, where the Nazca Plate subducts beneath the South American Plate at a convergence rate of about 6.6 cm per year. The tectonic regime produces frequent seismic events, with hypocenters commonly located at depths of 15–35 km along the plate interface and within the overriding crust.

Magnitudes during the swarm ranged from 3.0 to 5.1, with the largest event recorded at 01:46 UTC on 29 April. Depths clustered tightly between 18 and 28 km for most shocks, consistent with the geometry of the subduction interface in this segment. The temporal distribution showed peak activity on 28 April, followed by a gradual decline, typical of swarm behavior driven by fluid migration or aseismic slip rather than a single mainshock-aftershock sequence.

Valparaíso lies in one of Chile’s most earthquake-prone coastal zones. Historical records document major destructive events, including the 1906 Mw 8.2 earthquake and the 1985 Mw 8.0 event, both of which originated near the same offshore segment. Since 2000, seven swarms have been identified in the region, occurring in 2003, 2008, 2010 (two episodes), 2011, 2015, and 2017. These recurrent swarms highlight persistent stress accumulation and episodic release along the locked portion of the megathrust.

The 2017 swarm did not produce reported damage or tsunami alerts, reflecting the moderate energy release. Such sequences nevertheless provide valuable data on fault behavior and can precede larger events when they indicate accelerated slip. Ongoing monitoring by Chilean and international networks continues to track microseismicity in the area to refine probabilistic hazard assessments.

References

USGS Earthquake Catalog
Global CMT Catalog
Servicio Nacional de Geología y Minería (SERNAGEOMIN) reports