The 2005 Tarapacá Earthquake and Northern Chile's Subduction Zone Dynamics

Northern Chile occupies a tectonically active segment of the Pacific Ring of Fire, where the Nazca plate subducts beneath the South American plate at rates of 6–7 cm per year. This convergent margin produces frequent intermediate-depth earthquakes within the descending slab, alongside occasional megathrust events at the plate interface. The region around Iquique lies within the Andean volcanic arc and forearc, characterized by thick continental crust and a history of both intraslab and interface seismicity. On 13 June 2005 at 22:44 UTC, a magnitude 7.8 earthquake struck approximately 102 km east-northeast of Iquique. The event occurred at a focal depth of 115.6 km, placing it well within the subducting Nazca slab. Its epicentral location near Tarapacá aligns with the broader pattern of intermediate-depth seismicity driven by slab dehydration and phase changes at depths exceeding 100 km. No significant surface rupture occurred, consistent with the event's intraslab origin rather than a shallow thrust mechanism. Since 2000, this earthquake remains the sole magnitude 7.8 event recorded in the immediate vicinity, underscoring the episodic nature of large intraslab ruptures in northern Chile. The region's seismic record includes earlier destructive events, such as the 1877 Iquique earthquake, which generated a major tsunami, and the 2001 Arequipa earthquake to the north. These events illustrate the dual hazards of deep intraslab quakes and shallower interface ruptures capable of producing tsunamis. Geological studies of the area highlight the role of the subducting plate's geometry, including variable dip angles and the presence of the Iquique Ridge, which influences local stress accumulation. Updated seismic monitoring by international networks continues to refine models of slab-related seismicity, aiding hazard assessment for coastal communities.

References

USGS Earthquake Catalog Global CMT Project Servicio Sismológico Nacional de Chile reports