The 1960 Valdivia Earthquake

The most powerful earthquake ever recorded by instruments struck southern Chile on the afternoon of May 22, 1960. Seismologists rate it at magnitude 9.4 to 9.6, and the US Geological Survey gives 9.5. For about ten minutes a section of the plate boundary roughly 1,000 kilometers long slipped, lowering parts of the coast by as much as two meters and drowning farmland and forest. A tsunami struck the Chilean coast within minutes and then crossed the Pacific, killing people in Hawaii, Japan and the Philippines up to a day later. The city of Valdivia, the largest town near the heaviest damage, gave the event its name, though Chileans often call it the Great Chilean Earthquake.

The epicenter lay inland of the coast of south-central Chile, about 185 kilometers north of Valdivia and some 525 kilometers south of Santiago, but the rupture ran south from the Arauco Peninsula almost to the Chiloé archipelago. It was the climax of a sequence that began on May 21 with a magnitude 8.1 foreshock near Concepción. The quake struck on the subduction zone where the Nazca Plate dives beneath the South American Plate at about 7 centimeters a year, the same boundary that raised the Andes. Waves up to about 25 meters high struck the coast. Some 15 hours later the tsunami reached Hilo, Hawaii, killing 61 people, and after about 22 hours it reached Japan, where some 140 died. Two days after the main shock, the Cordón Caulle volcanic complex began to erupt.

Estimates of the death toll vary widely, from about 1,000 to 6,000, with the US Geological Survey citing 1,655 for Chile. The toll was low for so vast a quake because the region was thinly populated, the shock came in mid-afternoon, and the previous day's foreshock had already driven many people outdoors. Around two million people lost their homes. A landslide dammed the outlet of Lake Riñihue, and workers spent about two months, in an effort remembered as the Riñihuazo, draining it gradually before it could burst over Valdivia. The quake let scientists record the free oscillations of the whole Earth clearly for the first time, and the deaths in Hawaii and Japan led to the Pacific-wide tsunami warning system set up in 1965 under UNESCO.

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• Chile
  A ribbon of land between the Andes and the Pacific located in
• The Ring of Fire
  The Pacific rim of subduction, where the ground does not hold still located in
• The Tectonic Plates
  The seven great slabs and dozens of smaller ones that make up Earth's moving shell Nazca–South American plate boundary
• Andes
  The world's longest continental mountain range, the 7,000-km spine of South America on the subduction zone that raised
• Pacific Ocean
  Earth's largest and deepest ocean tsunami crossed
• Hawaiian Islands
  A volcanic chain in the central Pacific, the most isolated archipelago on Earth tsunami struck
• Japan
  An archipelago empire of volcanoes, technology, and deep tradition tsunami struck