Location:

Period:

12 Oct 2006 18:24:08 - 16 Oct 2006 07:24:19 (3 days 13 hours)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 8.3; 48 km W of Illapel, Chile; (16 Sep 2015) (10km from the swarm center)

7 swarms found nearby.

2007

PS20070329.1(26.0km)

29 Mar

3 hours

6 earthquakes

2015

PS20150916.2(24.7km)

16 Sep

1 day 14 hours

48 earthquakes

PS20150917.1(71.4km)

16 Sep

4 hours

8 earthquakes

S20150917.1(12.6km)

16 Sep

3 days 1 hours

40 earthquakes

PS20150917.2(101.9km)

17 Sep

21 hours

9 earthquakes

PS20150919.1(101.9km)

19 Sep

1 day 12 hours

10 earthquakes

PS20150921.1(18.3km)

21 Sep

1 day 1 hours

7 earthquakes

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Seismic Swarm Near Illapel, Chile: October 2006 Event Analysis

SeismoSight recorded Swarm S20061013.1 beginning at 18:24 on 12 October 2006 and concluding at 07:24 on 16 October 2006. The sequence occurred 55 km west-northwest of Illapel, Chile, and comprised 50 earthquakes over 85 hours. Magnitudes ranged from 2.6 to 5.3, with focal depths between 6 km and 38 km. The largest event reached magnitude 5.3 at 16:12 on 13 October 2006.

The swarm displayed typical characteristics of clustered seismicity in a subduction setting. Early activity on 12 October featured several magnitude 3.0–4.1 events at depths of 14–38 km. Activity continued steadily through 13 October, including the peak magnitude 5.3 shock at 29 km depth. Subsequent days showed a gradual decline in both frequency and maximum magnitude, with the final recorded event at magnitude 2.9 on 16 October. Depths remained predominantly in the 10–30 km range, consistent with interface and intraslab sources.

Illapel lies within the central Chile seismic gap along the Peru-Chile Trench, where the Nazca plate subducts beneath the South American plate at approximately 6–7 cm per year. This convergent margin produces frequent megathrust earthquakes and associated swarms. The 2006 sequence occurred within a segment that later hosted the 16 September 2015 magnitude 8.3 Illapel earthquake, centered 48 km west of Illapel and roughly 10 km from the swarm centroid.

Regional seismic history includes multiple great earthquakes. The 2010 Maule event (magnitude 8.8) ruptured south of the area, while the 2015 Illapel mainshock filled part of the same central segment. Paleoseismic records indicate recurrence intervals of 80–150 years for magnitude 8+ events in this latitude band. Intermediate-depth seismicity is also common due to slab dehydration and bending stresses.

The 2006 swarm provides insight into precursory or background activity preceding larger ruptures. Its spatial overlap with the 2015 epicentral zone suggests possible stress migration or fluid involvement along the plate interface. Most events clustered at crustal and upper-slab depths, indicating a mix of interface slip and crustal fracturing. No surface rupture or significant damage was associated with the swarm, which remained below the threshold for widespread felt effects.

Seismic monitoring in central Chile has improved markedly since 2006 through expanded networks operated by the University of Chile and international collaborations. Such data enable refined understanding of swarm dynamics and their relation to the seismic cycle.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Servicio Sismológico Nacional, Universidad de Chile