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Earthquakes and South America

Thousands a Year!

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I was a young girl in Chile when the earthquake, called the largest earthquake of all time, hit in the southern portion of the country. On May 22, 1960, 19:11:14 UTC, a 9.5 earthquake struck 180 feet below the bottom of the sea and 100 miles off the Chilean coast near Valdivia.

Thanks to earlier alerts, there was not a large loss of life in Chile, but the resulting tsunamis caused damage along the Chilean and Peruvian coasts and spread across the entire Pacific Ocean to Hawaii, the Philippines, and Japan, with waves measuring up to 25 meters high. When the tsunami hit Onagawa, Japan almost 22 hours after the quake, a tide guage recorded a wave height of 10 feet above high tide. See Valdivia and the Catastrophe for details.

Some people regard earthquakes as occasional events, but over one million earthquakes happen every year. Some are so slight they are unfelt, others last for minutes that seem like forever and can cause major changes in the landscape. Others are huge catastrophic events that cause massive destruction and loss of life while forever changing the area and the people who lived there.

There are two major regions worldwide of earthquake, or terremoto, activity. One is the circum-Pacific belt which encircles the Pacific Ocean, affecting the West coasts of North America and South America, Japan, and the Phillipines. It includes the Ring of Fire along the Northern edges of the Pacific. The other is the Alpide belt which slices through Europe and Asia. It is along this line that the Christmas Sumatra earthquake occurred.

Earthquakes along these belts occur when two tectonic plates, far under the surface of the earth, collide, spread apart or slide past each other. This can happen very slowly, or quickly. Thee result of this faster activity is a sudden release of a tremendous release of energy that changes into wave movement. These waves roll through the earth’s crust, causing earth movement. As a result, mountains rise, ground falls or opens. Buildings near this activity can collapse, bridges can snap under the pressure and people can die.

If the earthquake occurs near or under water, the motion causes the wave action known as a tsunami. These waves are incredibly fast and dangerous. The tsunami from the December, 2004 Indian Ocean earthquake makes this the dealiest tsunami in history.

In South America (see current earthquake map), the portion of the circum-Pacific belt includes the Nazca and South American plates. About three inches of motion occurs between these plates each year. This motion results in three different, but interrelated ways:

  • About 1.4 inches of the Nazca plate slides smoothly under South America, creating deep pressure that gives rise to volcanoes.
  • Another 1.3 inches is locked up at the plate boundary, squeezing South America, and is released every hundred years or so in great earthquakes.
  • About a third of an inch crumples South America permanently, building the Andes.
    Studying Earthquakes By Satellite

    The Richter Magnitude Scale is a number that is used to measure the size of an earthquake. The magnitude is a measure on a seismograph of the strength of the seismic waves sent out from the focus, or the point of the actual rock rupture beneath the surface of the earth. The point directly above the focus on the surface is the epicenter. Each number on the Richter Magnitude Scale represents an earthquake that is thirty-one times as powerful as the preceding whole number, but is not used to assess damage, but Magnitude and Intensity. The scale has been revised so that there is no longer a higher limit. Recently, another scale called the moment magnitude scale has been devised for more precise study of great earthquakes.

    According to the USGS (United States Geological Survey} among the largest earthquakes since 1900, several were in South America:

  • Chile, ranked largest with a 9.5 rating, occurring in 1960
  • Off the coast of Ecuador, near Esmeraldas on January 31, 1906 with a magnitude of 8.8. This earthquake produced a 5-m local tsunami that destroyed 49 houses and killed 500 people in Colombia. It was recorded at San Diego and San Francisco, where an earthquake in April of the same year had a magnitude of 7.8.
  • On August 17, 1906 an 8.2 quake in Chile all but destroyed Valparaiso.
    Additionally, other significant quakes:
  • A May 31, 1970 earthquake in Peru with a magnitude of 7.9 killed 66,000 and caused $530,000 damage with a great rock slide and floods, destroying again the village of Ranrahirca which had been buried by a massive avalanche of rocks and ice from Cerro Huascaran in 1962
  • On July 31, 1970 a 8 magnitude earthquake struck Colombia
  • On June 9, 1994 Bolivia suffered an 8.2 quake {li]On January 25, 1999, a 6.2 quake hit Colombia
  • Coastal Peru was stuck by a 7.5 quake on June 23, 2001
  • On November 15, 2004 a 7.2 earthquake struck off the west coast of Colombia, near Chocó
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