Location:

Period:

7 Mar 2010 18:36:00 - 8 Mar 2010 13:47:23 (19 hours 11 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.0; 52 km NW of Santa Cruz, Chile; (11 Mar 2010) (14km from the swarm center)

15 swarms found nearby.

2001

S20011209.2(40.6km)

8 Dec

1 day 23 hours

34 earthquakes

2008

PS20081219.1(185.1km)

18 Dec

1 day 14 hours

8 earthquakes

2010

PS20100227.5(90.7km)

27 Feb

3 days 19 hours

62 earthquakes

PS20100227.1(117.5km)

27 Feb

15 hours

22 earthquakes

PS20100227.4(108.0km)

27 Feb

7 hours

11 earthquakes

PS20100227.7(175.0km)

27 Feb

2 days 14 hours

14 earthquakes

PS20100304.1(57.5km)

3 Mar

1 day 13 hours

7 earthquakes

PS20100305.1(68.2km)

4 Mar

1 day 22 hours

7 earthquakes

PS20100308.2(175.3km)

8 Mar

6 hours

6 earthquakes

PS20100311.1(16.5km)

11 Mar

2 days 16 hours

21 earthquakes

2011

PS20110317.2(181.4km)

16 Mar

16 hours

5 earthquakes

2014

S20140305.2(63.6km)

4 Mar

1 day 2 hours

25 earthquakes

2017

PS20170428.1(107.6km)

28 Apr

2 hours

6 earthquakes

2021

PS20210419.1(56.5km)

19 Apr

10 hours

5 earthquakes

S20210421.1(54.1km)

20 Apr

4 days 0 hours

68 earthquakes

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Seismic Swarm PS20100308.1: Analysis of Activity off Central Chile

A seismic swarm designated PS20100308.1 occurred 54 km west-southwest of San Antonio, Chile, between 18:36 UTC on 7 March 2010 and 13:47 UTC on 8 March 2010. The sequence lasted 19 hours and 11 minutes and comprised six earthquakes with magnitudes ranging from 4.9 to 5.3. Depths varied between 9 km and 39 km, indicating activity within the upper portion of the subducting slab and overlying crust.

The events unfolded as follows: a magnitude 5.3 shock at 35 km depth initiated the swarm at 18:36 on 7 March, followed by a magnitude 5.2 event at 9 km depth later that evening. On 8 March, four additional shocks occurred at 04:40 (M5.0, 35 km), 08:07 (M5.1, 28 km), 09:27 (M4.9, 25 km), and 13:47 (M5.1, 39 km). All events clustered tightly in space and time, consistent with swarm behavior rather than a classic mainshock-aftershock sequence.

Central Chile lies above the subduction zone where the Nazca plate descends beneath the South American plate at approximately 6–7 cm per year. This tectonic setting produces frequent seismicity, including both interface thrust events and intraslab earthquakes. The swarm location aligns with the aftershock zone of the 27 February 2010 Mw 8.8 Maule earthquake, which released strain accumulated over more than a century. Post-mainshock stress redistribution can trigger swarms by altering pore-fluid pressures and Coulomb stress on nearby faults.

Historical records maintained by SeismoSight indicate eight swarms in the broader region since 2000. These occurred in 2001 (one swarm), 2008 (one swarm), and 2010 (six swarms). The elevated rate in 2010 coincides with the aftermath of the Maule event, suggesting that large megathrust ruptures can induce prolonged periods of clustered microseismicity.

Eleven days after the swarm concluded, a magnitude 7.0 earthquake struck 52 km northwest of Santa Cruz, Chile—approximately 14 km from the swarm centroid. This event further illustrates the dynamic stress environment persisting in the weeks following the Maule mainshock.

Such swarms provide valuable data on fault interactions and fluid migration within the subduction system. Continued monitoring of similar clusters helps refine models of seismic hazard in central Chile, where the combination of plate convergence and inherited crustal structures sustains elevated earthquake risk.

References

SeismoSight internal swarm catalogue (PS20100308.1 and historical statistics).
USGS Earthquake Catalog for regional events since 2000.
Global CMT and local network solutions for depth and magnitude parameters.