Seismic Swarm PS20100227.4: Analysis of Events Near Constitución, Chile

A seismic swarm designated PS20100227.4 was recorded on 27 February 2010 near Constitución, Chile. The sequence began at 06:56 and concluded at 14:29, spanning 7 hours and 32 minutes. Eleven earthquakes were registered during this period, with epicenters located approximately 32 km northeast of Constitución.

The events exhibited magnitudes ranging from 4.7 to 6.0 and focal depths between 10 km and 35 km. The strongest shock reached magnitude 6.0 at 07:12:28, while the shallowest occurred at 14:29:03 with a depth of 10 km. These parameters indicate activity within the crustal and upper subduction interface zones typical of the region.

Geological Context

The area lies along the convergent margin where the Nazca Plate subducts beneath the South American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent megathrust earthquakes and associated aftershock sequences. The Constitución vicinity forms part of the Maule seismic gap, a segment of the plate boundary that had accumulated significant strain prior to major ruptures.

Historical records show that the region has experienced repeated large-magnitude events, consistent with the cyclic nature of subduction-zone seismicity. The swarm occurred within a zone of elevated post-seismic stress transfer following the magnitude 8.8 Maule earthquake earlier that day.

Regional Earthquake History

Since 2000, two swarms have been documented in the broader area, with the first occurring in 2010. Notable strong earthquakes near the swarm center include a magnitude 7.1 event on 25 March 2012 located 23 km northeast of Constitución and a magnitude 7.0 shock on 11 March 2010 situated 52 km northwest of Santa Cruz. Both events underscore the persistent seismic hazard along this segment of the margin.

Swarm Characteristics and Implications

The temporal clustering of eleven events within a narrow window, without a single dominant mainshock, aligns with swarm behavior driven by fluid migration or stress redistribution along pre-existing faults. Depths predominantly between 20 km and 35 km suggest involvement of both the plate interface and overlying crustal structures. Such sequences contribute to refined understanding of aftershock productivity and the potential for triggered seismicity in subduction environments.

Monitoring data from this swarm provide valuable constraints on local fault mechanics and stress evolution in the days immediately following the 2010 mainshock.

References

USGS Earthquake Catalog
Global CMT Catalog
Chilean Seismological Service (SSN) reports