Location:

Period:

7 Jul 2001 09:38:43 - 7 Jul 2001 21:27:33 (11 hours 48 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.6; 51 km SW of Punta de Bombón, Peru; (7 Jul 2001) (24km from the swarm center)

No swarms nearby.

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Seismic Swarm Activity Near Matarani, Peru in July 2001

On July 7, 2001, a seismic swarm designated PS20010707.1 was recorded 47 km south-southwest of Islay (Matarani), Peru. The sequence began at 09:38 and concluded at 21:27, encompassing six earthquakes within 11 hours and 48 minutes. The events occurred at shallow depths of 31–33 km, consistent with interface seismicity along the subduction boundary.

The largest event reached magnitude 7.6 at 09:38:43, followed by five aftershocks: magnitudes 5.1, 5.2, 4.7, 5.2, and 5.0. This swarm represents the sole seismic swarm documented in the region since January 1, 2000, with the prior comparable activity also occurring in 2001. A magnitude 7.6 earthquake located 51 km southwest of Punta de Bombón (approximately 24 km from the swarm centroid) aligns closely with the primary swarm event.

The Matarani area lies within the tectonically active forearc of southern Peru, where the Nazca Plate subducts beneath the South American Plate at rates of approximately 6–7 cm per year. This convergent margin produces frequent moderate-to-large earthquakes along the megathrust interface. Historical records indicate recurrent seismicity in the Arequipa region, driven by the geometry of the subducting slab and the presence of structural heterogeneities such as the Nazca Ridge.

Seismic swarms in subduction zones often reflect fluid migration or localized stress transfer following a mainshock. The July 2001 sequence followed the major June 23, 2001, magnitude 8.4 Peru earthquake by two weeks, suggesting possible triggering through afterslip or viscoelastic relaxation. Depths near 33 km place the activity at the plate interface, a zone prone to both thrust and intraslab events.

Regional monitoring since 2000 highlights the relative rarity of swarm-type behavior compared with isolated mainshock-aftershock sequences. Continued subduction drives long-term seismic hazard, with the potential for both interface and crustal events affecting coastal infrastructure and populations near Matarani and Punta de Bombón.

References

USGS Earthquake Catalog Global CMT Project Peru Subduction Zone Studies (various peer-reviewed publications)