The 2000 Deep-Focus Earthquake Near Añatuya, Argentina

On 23 April 2000 at 09:27 UTC, a magnitude 7.0 earthquake struck 22 km northwest of Añatuya in Santiago del Estero Province, Argentina. The event occurred at a focal depth of 608.5 km, classifying it as a deep-focus earthquake within the subducting Nazca Plate. No significant surface damage or casualties were reported, consistent with the attenuation of seismic energy from such extreme depths.

The seismicity of northwestern Argentina is driven by the ongoing subduction of the Nazca Plate beneath the South American Plate along the Andean margin. In this region the slab descends at a moderate angle before steepening, allowing brittle failure to persist to depths exceeding 600 km. Intermediate- and deep-focus events are therefore common, although magnitudes above 7.0 remain infrequent. The 2000 Añatuya earthquake is the sole magnitude-7.0 or greater event recorded in the area since 1 January 2000.

Geologically, Añatuya lies within the Chaco-Pampean plain east of the Andean orogen. The subsurface is characterized by a thick sequence of Quaternary and Neogene sediments overlying Precambrian basement. The earthquake hypocenter was located well within the oceanic lithosphere of the Nazca Plate, far below these surface units. Focal mechanisms for similar deep events in the region typically indicate downdip tension or compression, reflecting stresses transmitted through the cold slab interior.

Historically, Argentina has experienced several notable deep earthquakes. The 1994 Bolivia event (Mw 8.2, depth 647 km) and earlier 20th-century shocks near the Chile-Argentina border illustrate the capacity of the subducting slab to generate large-magnitude seismicity at great depth. The 2000 Añatuya earthquake fits this pattern, providing additional data on slab rheology and phase transitions at the base of the mantle transition zone.

Seismic monitoring by the U.S. Geological Survey and the Argentine National Institute of Seismic Prevention continues to track activity along the Andean subduction zone. Updated catalogs confirm that no subsequent event of comparable magnitude has occurred in the immediate vicinity of Añatuya through the present.

References

U.S. Geological Survey Earthquake Catalog
Argentine National Institute of Seismic Prevention (INPRES) reports
Global CMT Project focal-mechanism database