(64).Earthquake zone

What caused the 2010 earthquake in Angol, Chile?

Angol, Chile, experienced a huge 8.8 magnitude earthquake in February 2010. The earthquake was due to subduction of the Nazca plate beneath South America. This subduction zone is part of the Pacific Ring of Fire.

Annual Earthquakes

In a single year, on average, more than 900,000 earthquakes are recorded. About 150,000 of them are strong enough to be felt. Each year about 18 earthquakes are major, with a Richter magnitude of 7.0 to 7.9, and on average one earthquake has a magnitude of 8 to 8.9.

Magnitude 9 earthquakes are rare. The United States Geological Survey lists five since 1900 (Figure below and Tablebelow). All but the Great Indian Ocean Earthquake of 2004 occurred somewhere around the Pacific Ocean basin.

[Figure 1]

The 1964 Good Friday Earthquake centered in Prince William Sound, Alaska released the second most amount of energy of any earthquake in recorded history.

LocationYearMagnitudeValdivia, Chile19609.5Prince William Sound, Alaska19649.2Great Indian Ocean Earthquake20049.1Kamchatka, Alaska19529.0Tōhoku, Japan20119.0

Earthquake Zones

Nearly 95% of all earthquakes take place along one of the three types of plate boundaries.

About 80% of all earthquakes strike around the Pacific Ocean basin because it is lined with convergent and transform boundaries (Figurebelow). The region around the Pacific is called the Pacific Ring of Fire due to its earthquakes and volcanoes.

About 15% take place in the Mediterranean-Asiatic Belt. Convergence is causing the Indian Plate to run into the Eurasian Plate.

The remaining 5% are scattered around other plate boundaries. A few earthquakes take place away from plate boundaries. These are intraplate earthquakes.

[Figure 2]

Earthquake epicenters for magnitude 8.0 and greater events since 1900. The earthquake depth shows that most large quakes are shallow focus, but some subducted plates cause deep focus quakes.

Summary

Small earthquakes are extremely common, but the largest earthquakes are extremely rare.

The vast majority of earthquakes happen at plate boundaries.

The Pacific Ocean basin has the most earthquakes due to convergent and transform plate boundaries. The Himalaya region has the second most due to the convergence of India and Asia.