Seismic Swarm PS20100305.1: Analysis of Activity Near Santa Cruz, Chile

A seismic swarm designated PS20100305.1 occurred approximately 45 km west-northwest of Santa Cruz, Chile, between 04:23 UTC on 4 March 2010 and 03:09 UTC on 6 March 2010. Over this 46-hour period, seven earthquakes were recorded, with magnitudes ranging from 5.0 to 5.8 and focal depths between 8 km and 60 km. This sequence reflects typical clustered seismicity in a tectonically active subduction environment. The events unfolded as follows: two magnitude-5.1 shocks at 35 km depth on 4 March, followed on 5 March by a 5.4 event at 8 km, a 5.8 event at 60 km, a 5.3 event at 34 km, and a 5.0 event at 35 km; the sequence concluded with a magnitude-5.0 shock at 15 km depth early on 6 March. Such rapid succession of moderate events without a single dominant mainshock is characteristic of swarm behavior driven by fluid migration or stress redistribution along fault interfaces. Chile’s central region lies within the Andean subduction zone, where the Nazca Plate converges with the South American Plate at rates exceeding 6 cm per year. This setting produces frequent intermediate-depth and crustal earthquakes. The swarm location aligns with the aftershock zone of the great 27 February 2010 Maule earthquake (Mw 8.8), whose post-seismic relaxation likely influenced local stress fields and triggered the observed activity. Historical records since 2000 indicate seven prior swarms in the broader area, with one occurring in 2001 and six in 2010. Notable larger events nearby include the Mw 7.0 earthquake of 11 March 2010 located 56 km from the swarm center and the Mw 7.1 event of 25 March 2012 situated 51 km away. These occurrences underscore the persistent seismic hazard along this segment of the margin. Seismic swarms in subduction zones often serve as indicators of evolving fault conditions and can precede or accompany major strain release. Continued monitoring remains essential for assessing whether similar clusters may recur in this highly active corridor. References
SeismoSight internal swarm catalog PS20100305.1.
USGS Earthquake Catalog (events since 2000).
Global CMT Project (regional moment tensor solutions).