Seismic Swarm PS20100313.1: Geological Context Near Lebu, Chile
A seismic swarm designated PS20100313.1 occurred 15 km east-northeast of Lebu, Chile, on 13 March 2010. The sequence began at 03:15 UTC and concluded at 20:20 UTC, encompassing six earthquakes within a 17-hour period. This activity took place in a tectonically active segment of south-central Chile, two weeks after the Mw 8.8 Maule megathrust earthquake of 27 February 2010.
Lebu lies within the Bio-Bío Region, positioned above the subduction interface where the Nazca Plate descends beneath the South American Plate along the Peru-Chile Trench. Convergence rates average 6–7 cm per year, driving recurrent large-magnitude events and associated aftershock sequences. Focal depths of the swarm events ranged from 15 km to 40 km, consistent with the depth range of the plate interface and overlying crustal stresses in this sector.
The recorded events displayed the following parameters: a magnitude 5.3 earthquake at 15 km depth at 03:15, followed by magnitude 5.4 and 5.3 shocks at 30 km and 40 km depths minutes later. Later activity included a magnitude 5.8 event at 35 km depth at 10:34, a magnitude 4.7 event at the same depth at 10:39, and a final magnitude 5.3 earthquake at 37 km depth at 20:20. These magnitudes and depths align with typical aftershock behavior in the region, reflecting stress redistribution along the ruptured fault segments.
Chile’s subduction margin has produced some of the largest instrumentally recorded earthquakes, including the 1960 Valdivia event. Post-2010 monitoring has refined understanding of aftershock migration patterns, with swarms often occurring near the edges of mainshock rupture zones. The Lebu area sits near the southern limit of the 2010 rupture, where heterogeneous frictional properties can promote clustered seismicity.
Since 1 January 2000, six swarms have been identified in the regional catalog according to internal classification criteria, with the earliest occurring in 2010. Such sequences provide data on fault interactions and post-seismic relaxation processes in subduction environments.
Ongoing seismic networks operated by Chilean institutions continue to track activity in this zone, contributing to improved hazard assessment for coastal communities.
References
United States Geological Survey Earthquake Catalog
Global CMT Project
Servicio Nacional de Geología y Minería (SERNAGEOMIN) reports on Chilean seismicity