Yesterday's earthquake in central Peru developed along a subduction zone. The Nazca Plate, a remnant of the Farallon Plate, is being pushed beneath the South American Plate. In such collision zones, the edge of the upper plate (in this case the South American Plate) is forced downward by friction between the plates; on occasion, this building pressure is released, the plate slips upward and an earthquake results.
Centered 90 miles SSE of Lima and 25 miles beneath the surface of the sea, the 7.9 magnitude quake lasted 2 minutes and was followed by at least 11 aftershocks; a small tsunami was also triggered by the quake. Peru officials report more than 330 dead and at least 1200 injured.
This subduction process along the west coast of South America has been going on for at least 180 million years and is responsible for the development of the Andes. As the Nazca Plate moves deeper beneath the Continental Plate of South America, it approaches the Earth's mantle and is melted, producing a chain of volcanoes at the surface. Part of the Pacific "Ring of Fire," volcanism and earthquakes will continue in this region until the entire Nazca Plate is consumed.
