Location:

Period:

28 Oct 2011 18:54:34 - 28 Oct 2011 23:46:01 (4 hours 51 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

4 swarms found nearby.

2007

PS20070628.1(170.1km)

28 Jun

17 hours

6 earthquakes

PS20070816.1(112.9km)

15 Aug

3 days 20 hours

28 earthquakes

PS20070816.2(42.6km)

16 Aug

8 hours

6 earthquakes

2022

PS20221029.1(27.4km)

28 Oct

1 day 6 hours

6 earthquakes

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Seismic Swarm PS20111028.1: Analysis of Events Near Santiago, Peru

On 28 October 2011, a seismic swarm designated PS20111028.1 was recorded 38 km SSW of Santiago, Peru. The sequence began at 18:54 and concluded at 23:46 local time, spanning 4 hours and 51 minutes. During this period, five earthquakes were registered, providing insight into short-term clustered seismic activity in the region.

The events unfolded as follows. The initial shock at 18:54 measured magnitude 6.9 at a depth of 24 km. Approximately seven minutes later, a magnitude 5.6 event occurred at 22 km depth. A magnitude 5.0 earthquake followed at 19:10 at a shallow depth of 8 km. Later activity included another magnitude 5.0 event at 22:00 at 25 km depth, and the sequence ended with a magnitude 5.6 shock at 23:46 at 10 km depth. These events illustrate typical swarm characteristics, with rapid succession of moderate to strong tremors at varying depths.

Peru lies along the convergent boundary where the Nazca Plate subducts beneath the South American Plate at rates of approximately 6–10 cm per year. This tectonic setting drives frequent seismicity, particularly in the coastal and Andean zones. Santiago is situated in a region influenced by both the subduction megathrust and shallower crustal faults. Depths recorded in the swarm align with known patterns of interface and intraslab earthquakes in central Peru.

The area has experienced significant historical earthquakes linked to the same subduction dynamics. Major events, such as the 1970 Ancash earthquake, underscore the potential for destructive shaking. Since 2000, three swarms have been documented in the broader region, with the earliest occurring in 2007. Such clusters may reflect episodic stress release along the plate interface without necessarily preceding a larger mainshock.

This swarm contributes to understanding localized seismic behavior in Peru’s subduction zone. Monitoring of depth variations and magnitude distributions aids in refining hazard assessments for nearby communities. Continued observation supports improved preparedness in a tectonically active environment.

References

USGS Earthquake Catalog (historical seismicity data for Peru subduction zone)
Global CMT Project (focal mechanism and depth characteristics of Andean events)
SeismoSight internal swarm classification records