Saturday, May 31, 2008

Earthquake Facts And Figures,Causes world Earthquakes

What is Earthquake?
An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasingy in waves that travel through the rock to cause the shaking that we feel during an earthquake.


Most Earthquakes Occur in the World

The surface of the earth is divided like a jigsaw puzzle into giant pieces called tectonic or crustal plates. These giant pieces move slowly over partially melted rock known as the mantle. As they move, they slide along each other, move into each other, move away from each other, or one slips under another. On these active plate boundaries about 95% of all the world's earthquakes occur. California, Alaska, Japan, South America, and the Philippines are all on plate boundaries. Only 5% are in areas of the plates far away from the boundaries. These are called mid-plate or intra-plate earthquakes and are, as yet, poorly understood.

There are over a million quakes annually, including those too small to be felt. The following table shows the average frequency of different magnitudes.
Description Magnitude Frequency per year
Great 8.0+ 1
Major 7.0-7.9 18
Large (destructive) 6.0-6.9 120
Moderate (damaging) 5.0-5.9 1,000
Minor (damage slight) 4.0-4.0 6,000
Generally felt 3.0-3.9 49,000
Potentially perceptible 2.0-2.9 300,000
Imperceptible less than 2.0 600,000+



Using the previous table:

Per month Approximately 80,000

Per day Approximately 2,600

Per minute Approximately 2

And, per second, one earthquake is felt approximately every 30 seconds.

Earthquakes Occur in the United States

Alaska has more earthquakes per year than the combined total of the rest of the United States. As many as 4,000 are recorded there every year. Alaska is on a plate boundary where one plate is sliding along another, a subduction zone.

Largest Known Earthquake

A magnitude 9.5 earthquake in Chile in 1960 was the largest known earthquake and resulted in over 6,000 deaths. It triggered a tsunami or seismic wave (incorrectly known as a tidal wave) that killed people as far away as Hawaii and Japan. Chile is also on a subduction zone.


2 Comments:

Siladitya said...

Post more about this topic.
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Sean Luke said...

This topic add reference for my future assignment. Thank you. Everyone can use this article to analyse what causes earthquakes. Another related topic on coverage: Where do earthquakes usually occur?

 

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