Seismic Swarm PS20100227.2: Aftershock Sequence of the 2010 Maule Earthquake

The seismic swarm designated PS20100227.2 began at 06:34 on 27 February 2010 and concluded at 15:52 on 1 March 2010. It was located 69 km northwest of Tomé, Chile, and produced 41 earthquakes over 57 hours and 18 minutes. This sequence occurred immediately following the Mw 8.8 Maule mainshock, whose epicenter lay approximately 95 km from the swarm centroid.

The Maule earthquake ruptured a roughly 500 km segment of the megathrust interface where the Nazca plate subducts beneath the South American plate at a convergence rate of about 66 mm per year. The event released strain accumulated since the great 1835 and 1906 ruptures in the same segment. Focal depths of the listed events range from 22 km to 48 km, consistent with the geometry of the plate interface and overlying crust in the region.

Geologically, central Chile forms part of the Andean subduction zone, one of the most seismically active margins on Earth. The margin exhibits a well-developed accretionary prism and forearc basin system, with the Coastal Cordillera exposing Paleozoic to Mesozoic metamorphic and igneous rocks. The Bio-Bío region near Tomé is underlain by the South American plate’s continental crust, which experiences both interplate thrust faulting and shallower intraplate normal faulting triggered by the mainshock’s stress changes.

The swarm comprised one Mw 8.8 event at 22 km depth, followed by 40 additional earthquakes, predominantly in the Mw 5.0–5.7 range and clustered between 24 km and 40 km depth. These events represent aftershocks that filled the rupture area and adjacent stress-loaded zones. The rapid onset and sustained high rate of moderate-magnitude activity are characteristic of aftershock sequences following great subduction earthquakes, where Coulomb stress increases promote failure on both the megathrust and subsidiary faults.

Chile’s historical record underscores the recurrence of great earthquakes. The 1960 Mw 9.5 Valdivia event, the 1985 Mw 8.0 Valparaíso earthquake, and the 2010 Maule event together illustrate the segmented nature of the margin and the potential for multi-segment ruptures. Post-2010 studies have refined slip models and identified areas of both high and low slip, helping explain the spatial distribution of the observed aftershocks.

Updated analyses from global seismic networks confirm that aftershock productivity remained elevated for weeks after the swarm period, gradually decaying according to Omori-law statistics. No significant change in regional strain accumulation rates has been detected since 2010, indicating that the Maule segment continues to reload.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Chilean Seismological Center (sismologia.cl)
Oncken et al., 2013, “Seismic Gap Revisited: The 2010 Maule Earthquake,” Tectonophysics.