The 2000 M7.2 Earthquake and Seismicity of the Andean Subduction Zone near San Antonio de los Cobres, Argentina

On 12 May 2000 at 18:43 UTC, a magnitude 7.2 earthquake struck 75 km north of San Antonio de los Cobres in northwestern Argentina. The event occurred at a focal depth of 225 km, placing it well within the subducting slab of the Nazca Plate beneath the South American Plate. This intermediate-depth earthquake exemplifies the seismic activity driven by ongoing plate convergence along the Andean margin. The region lies within the Central Andes, specifically the Puna-Altiplano plateau in Salta Province. Here, the Nazca Plate subducts eastward at an angle of approximately 30 degrees, generating a Wadati-Benioff zone that extends to depths exceeding 200 km. The high elevation of the plateau, averaging over 3,500 meters, results from crustal shortening and magmatic addition accumulated over the past 25 million years. Volcanic arcs and fault systems, including segments of the El Toro-Olacapato-Tarapaca fault zone, accommodate deformation and contribute to the area's elevated seismic hazard. Historical seismicity in this portion of the Andes reflects the persistent subduction process. Large intermediate-depth events have occurred periodically, with notable activity recorded in the 20th century. The 2000 earthquake stands as the strongest event in the immediate vicinity since the start of 2000, occurring directly within the subducted slab where phase changes in minerals can promote brittle failure at depth. No significant surface rupture was associated with the 2000 event due to its depth, though it was widely felt across northern Argentina, southern Bolivia, and parts of Chile. Such deep-focus earthquakes typically produce less intense ground shaking at the surface compared with shallow crustal events but can still pose risks to infrastructure in the remote highland communities. Ongoing monitoring by regional seismic networks continues to track activity along the subduction interface and within the descending slab. The interplay between plate convergence rates of roughly 6–7 cm per year and the complex geometry of the slab maintains the potential for future moderate-to-large earthquakes in this geologically active corridor of the Andes.

References

USGS Earthquake Catalog (event data for 12 May 2000).
Global CMT Project (focal mechanism and depth parameters).
Oncken, O., et al. (2006). The Andes: Active Subduction Orogeny, Springer.