Chile Earthquake - Saturday, February 27, 2010
>An 8.8 magnitude earthquake struck off the coast of central Chile early morning on Saturday, February 27, 2010 at 3:34 a.m. local time, about 200 miles southwest of the Chilean capital of Santiago, killing several hundred people and exposing millions of people to strong shaking that toppled many buildings.
Tsunami warnings were issued for Hawaii, as well as Australia, New Zealand, Indonesia, Japan, and other countries along the Pacific coastline, as the giant waves triggered by the earthquake reverberated through the entire ocean.
This earthquake occurred at the boundary between the Nazca and South American tectonic plates.( I have provided the picture at bottom) The two plates are converging at a rate of 80 mm per year. The earthquake occurred as thrust-faulting on the interface between the two plates, with the Nazca plate moving down and landward below the South American plate.
Coastal Chile has a history of very large earthquakes. Since 1973, there have been 13 events of magnitude 7.0 or greater. The February 27 shock originated about 230 km north of the source region of the magnitude 9.5 earthquake of May, 1960 -- the largest earthquake worldwide in the last 200 years or more.
Approximately 870 km to the north of the February 27 earthquake is the source region of the magnitude 8.5 earthquake of November, 1922. This great quake significantly impacted central Chile, killing several hundred people and causing severe property damage. The 1922 quake generated a 9-meter local tsunami that inundated the Chile coast near the town of Coquimbo; the tsunami also crossed the Pacific, washing away boats in Hilo harbor, Hawaii.
The magnitude 8.8 earthquake of February 27, 2010 ruptured the portion of the South American seduction zone separating these two massive historical earthquakes.
A large vigorous aftershock sequence can be expected from this earthquake.
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The 1960 Valdivia earthquake or Great Chilean Earthquake of 22 May 1960 is to date the most powerful earthquake ever recorded, rating 9.5 on the moment magnitude scale. It occurred in the afternoon and its resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia, and the Aleutian Islands in Alaska.
The epicenter was near Cañete (see map) some 900 km (435 miles) south of Santiago, although Valdivia, Chile was the most affected city. It caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,000 miles) from the epicenter, and as far away as Japan and the Philippines.
The earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca Plate and the South American Plate. The focus was relatively shallow at 33 km, considering that earthquakes in northern Chile and Argentina may reach depths of 70 km. Subduction zones are known to produce the strongest earthquakes on earth as their particular structure allows more stress to build up before energy is released.
Note - Megathrust earthquakes occur at subduction zones at destructive plate boundaries (convergent boundaries), where one tectonic plate is forced (or subducts) under another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all five earthquakes of magnitude 9.0 or greater have been megathrust earthquakes in fact, no other type of known tectonic activity can produce earthquakes of this scale.
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