Seismic Swarm PS20100310.1 Near Talcahuano, Chile

A seismic swarm designated PS20100310.1 occurred on 10 March 2010, approximately 7 km west-northwest of Talcahuano, Chile. The sequence began at 02:41 and concluded at 09:37, encompassing five earthquakes within a span of six hours and fifty-six minutes. These events reflect typical post-mainshock activity in a tectonically active subduction zone.

The individual earthquakes registered magnitudes between 5.0 and 5.2, with focal depths ranging from 10 km to 36 km. Specific occurrences included a magnitude 5.2 event at 02:41:48 (32 km depth), followed by another magnitude 5.2 at 04:01:48 (36 km depth). Later activity featured a magnitude 5.1 at 09:04:09 (27 km depth), a magnitude 5.0 at 09:04:10 (10 km depth), and a final magnitude 5.2 at 09:37:59 (35 km depth). Such clustered, moderate-magnitude events without a dominant mainshock characterize swarm behavior in this region.

This swarm represents the first recorded since 2000 in the local catalog, with four additional swarms documented through the present. Its timing aligns closely with the 27 February 2010 Maule earthquake of magnitude 8.8, centered 81 km away. The Maule event, resulting from thrust faulting along the Nazca-South American plate interface, triggered widespread aftershock sequences across central Chile. Swarms like PS20100310.1 likely stem from stress redistribution and fluid migration within the fractured crust following the mainshock.

The Talcahuano area lies within Chile's highly seismic Andean margin, where the Nazca plate subducts beneath the South American plate at rates of approximately 6–7 cm per year. This convergence has produced recurrent great earthquakes, including the 2010 Maule rupture that extended over 500 km along the plate boundary. Historical records indicate that such megathrust events recur every few centuries, with associated aftershock activity persisting for months to years.

Geological monitoring in the region emphasizes the role of swarm sequences in delineating fault segments and assessing ongoing seismic hazard. Depths between 10 km and 36 km correspond to the seismogenic zone where brittle failure predominates along the subduction interface and overlying crustal faults. Continued observation supports refined models of post-seismic relaxation in this convergent setting.

References

SeismoSight internal swarm classification records.
USGS Earthquake Catalog for Maule 2010 event parameters.
Global CMT Project for regional focal mechanism data.