Location:

Period:

19 Sep 2015 04:33:48 - 20 Sep 2015 17:18:28 (1 day 12 hours 44 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

9 swarms found nearby.

2003

S20030620.1(15.6km)

19 Jun

10 days 9 hours

233 earthquakes

2006

S20061013.1(101.9km)

12 Oct

3 days 13 hours

50 earthquakes

2007

PS20070329.1(113.2km)

29 Mar

3 hours

6 earthquakes

2015

PS20150916.2(83.2km)

16 Sep

1 day 14 hours

48 earthquakes

PS20150917.1(51.1km)

16 Sep

4 hours

8 earthquakes

S20150917.1(89.6km)

16 Sep

3 days 1 hours

40 earthquakes

PS20150917.2(192.3km)

17 Sep

21 hours

9 earthquakes

PS20150921.1(103.8km)

21 Sep

1 day 1 hours

7 earthquakes

PS20151111.1(119.9km)

11 Nov

1 hours

6 earthquakes

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Seismic Swarm PS20150919.1: Analysis of Activity West of Ovalle, Chile

Seismic swarm PS20150919.1 occurred 55 km west of Ovalle in Chile’s Coquimbo Region. The sequence began at 04:33 UTC on 19 September 2015 and concluded at 17:18 UTC on 20 September 2015, lasting 36 hours and 44 minutes. During this period, ten earthquakes were recorded, with magnitudes ranging from 4.2 to 6.1 and focal depths between 1 km and 45 km.

The largest event reached magnitude 6.1 at a depth of 6 km on 19 September at 05:06 UTC. Subsequent events included a magnitude 5.7 shock at 28 km depth and several magnitude 5.0–5.6 events clustered between 8 km and 10 km depth. The final event, magnitude 5.0, occurred at 35 km depth. These parameters indicate a mix of shallow crustal and intermediate-depth activity typical of the region’s tectonic setting.

Ovalle lies within the central segment of the Peru-Chile subduction zone, where the Nazca Plate converges with the South American Plate at approximately 6–7 cm per year. This tectonic environment produces frequent megathrust earthquakes and associated aftershock sequences or swarms. The Coquimbo Region has experienced elevated seismicity linked to the 2015 Illapel mainshock three days prior, which may have influenced local stress conditions.

Historical records maintained since 1 January 2000 document seven swarms in the immediate area. These occurred in 2003, 2006, 2007, and four separate episodes in 2015, underscoring the recurrent nature of clustered seismicity along this portion of the margin.

The 2015 swarm exhibited a rapid onset followed by a gradual decline in event rate, consistent with stress redistribution after a major subduction-zone rupture. Depths varied widely, suggesting activation of both the plate interface and overlying crustal faults. No surface rupture was reported, and the sequence remained below magnitudes capable of generating significant local damage.

Such swarms provide valuable data on fault interactions and post-seismic processes in subduction settings. Continued monitoring by regional networks helps refine hazard assessments for the Coquimbo Region, where population centers lie close to active seismic sources.

References

United States Geological Survey Earthquake Catalog
Global Centroid Moment Tensor Project
SeismoSight internal swarm classification database