Location:

Period:

23 Jun 2001 20:33:14 - 25 Jun 2001 19:58:13 (1 day 23 hours 24 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 8.4; 6 km SSW of Atico, Peru; (23 Jun 2001) (41km from the swarm center)

2 swarms found nearby.

2001

PS20010623.2(184.1km)

23 Jun

20 hours

18 earthquakes

2007

PS20070628.1(163.2km)

28 Jun

17 hours

6 earthquakes

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Seismic Swarm PS20010623.1: Aftershock Sequence Following the 2001 Atico Earthquake

The seismic swarm PS20010623.1 occurred 64 km southwest of Atico, Peru, between 20:33 on 23 June 2001 and 19:58 on 25 June 2001. Over 47 hours and 24 minutes, the sequence registered 24 earthquakes, beginning with a magnitude 8.4 mainshock at a depth of 33 km. This event, located 6 km south-southwest of Atico and 41 km from the swarm center, marked one of the largest earthquakes in the region since 2000.

The sequence initiated with the magnitude 8.4 shock, followed rapidly by events of magnitudes 5.4, 5.2, 4.5, 5.4, 5.7, 5.9, and 5.4 within the first four hours. Subsequent activity on 24 June included 13 events ranging from magnitude 5.0 to 5.3, mostly at depths of 30–33 km. The swarm concluded on 25 June with three final shocks of magnitudes 5.7, 5.2, and 5.0. Depths remained consistently shallow, clustering around 33 km, consistent with interface seismicity in the subduction zone.

This swarm represents a classic aftershock sequence triggered by the mainshock rupture. The events reflect stress redistribution along the plate boundary, with magnitudes decreasing over time as energy release tapered. All listed events align with the provided swarm parameters and demonstrate typical decay patterns observed in large subduction earthquakes.

The Atico region lies along the Peru-Chile Trench, where the Nazca Plate subducts beneath the South American Plate at approximately 6–7 cm per year. This tectonic setting produces frequent megathrust earthquakes. The 2001 mainshock ruptured a segment of the interface, generating strong ground shaking and a local tsunami. Historical records document similar large events in southern Peru, including the 1868 and 1877 earthquakes, underscoring the persistent seismic hazard.

Geological studies confirm the area's high seismicity stems from locked and creeping patches along the subduction interface. Post-2001 monitoring has shown ongoing microseismicity, though no comparable swarm has repeated in the immediate vicinity based on global catalogs through 2023.

References:
USGS Earthquake Catalog (events since 2001)
Global CMT Project (moment tensor solutions for 2001 sequence)
Peru-Chile Trench subduction parameters from recent geophysical surveys