The 2011 M7.0 Earthquake Near El Hoyo, Argentina: Deep Seismicity in the Andes

On January 1, 2011, at 09:56 UTC, a magnitude 7.0 earthquake struck 26 km north-northeast of El Hoyo, Argentina, at a focal depth of 576.8 km. This event represents the sole M7.0 or greater earthquake recorded in the region since January 1, 2000. Its extreme depth places the rupture well within the mantle, consistent with the tectonic setting of the central Andes. The epicentral area lies in northwestern Argentina, within the Andean back-arc domain influenced by the ongoing subduction of the Nazca Plate beneath the South American Plate. Subduction along this margin occurs at rates of approximately 6–7 cm per year, driving both shallow crustal deformation and deep seismicity. Earthquakes at depths exceeding 500 km occur when the subducting slab remains sufficiently cold and brittle to generate brittle failure in the mantle transition zone. The 576.8 km depth of the 2011 event aligns with the expected geometry of the Nazca slab, which descends steeply beneath the Andean orogen before flattening in some segments farther east. Geologically, the region around El Hoyo features Paleozoic to Cenozoic sedimentary and volcanic sequences overlying Precambrian basement. The Andean orogeny has produced thick-skinned thrusting, foreland basins, and localized extension. Historical seismicity in northwestern Argentina includes destructive shallow events such as the 1944 San Juan earthquake, yet deep-focus activity like the 2011 event rarely produces surface damage due to energy dissipation over hundreds of kilometers. No significant aftershocks or surface rupture were reported for this earthquake, as expected for an intraslab event at such depth. Seismic monitoring indicates that deep earthquakes in this segment of the Andean margin occur sporadically, often clustered along the Wadati-Benioff zone. The 2011 event underscores the capacity of the subducting slab to store and release elastic strain at mantle depths, contributing to the overall seismic hazard characterization of the central Andes. Ongoing geodetic and seismological studies continue to refine slab geometry and rheology in this tectonically active corridor.

References

USGS Earthquake Catalog (prompt data)
Global CMT Project
Argentine National Seismic Network reports