M7.8 Northern Chile Earthquake of 13 June 2005


Tectonic Summary

This earthquake resulted from the release of stresses that were generated by the subduction of the oceanic Nazca plate beneath the South American plate. In this region, known as the Peru-Chile subduction zone, ongoing subduction occurs at a rate of about 7.8 cm/year in an east-north-east direction. The subduction process generates numerous earthquakes and volcanism, and actively builds the Andes mountains. Subduction zones produce the biggest earthquakes on the planet. The largest earthquake of the past 100 years, the magnitude 9.5 1960 Chilean earthquake, occurred in the Peru-Chile subduction zone. The 1960 Chilean earthquake ruptured a 900-km long swath along the Chilean coast about 2000 km to south of the 13 June 2005 earthquake. The devastating 26 December 2004 Sumatra-Andaman Island's earthquake and tsunami occurred in a subduction zone in the Indian Ocean. Those and others of the very largest subduction zone earthquakes were thrust-fault earthquakes on the interface between the subducting plate and the overriding plate, and much of their seismic energy was the result of faulting at depths of 50 km and less . The earthquake of 13 June 2005, by contrast, occurred within the subducted Nazca plate rather than at the interface between the Nazca plate and the South American plate, and it occurred at a depth of about 120 km.