# 7 Things You Didn’t Know About Earthquakes

1. Unsteady Ground An earthquake happens somewhere every single day. The U.S. Geological Survey (USGS) estimates that several million earthquakes

An earthquake happens somewhere every single day. The U.S. Geological Survey (USGS) estimates that several million earthquakes occur in the world each year. Many go undetected because they hit remote areas or have very small magnitudes. The National Earthquake Information Center (NEIC) locates about 50 earthquakes every day, or about 20,000 a year.

2. A Look at 2009
At least 1,783 deaths worldwide resulted from earthquake activity in 2009.

3. The Richter Scale
Charles F. Richter developed the scale in 1935 as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is recorded by a seismograph. When an earthquake begins, the base of the seismograph shakes but a hanging weight does not. A spring absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded, according to the U.S. Geological Survey.

4. History’s Most Devastating Quake
The largest earthquake in recorded history struck Chile in 1977. It measured 9.5 on the Richter scale.

5. Are the Number of Earthquakes Increasing?
The number of large earthquakes constituted as 6.0 and greater has stayed relatively constant. Since 1900, scientists expect about 17 major earthquakes, (magnitude 7.0 – 7.9) and one great earthquake (8.0 or above) in any given year. The devastating earthquake in Haiti in 2010 was 7.0 and the 2011 earthquake in Japan was 9.0.

6. How Can You Keep Track?
Find out about the last earthquake in your state at the USGS site. You may be surprised how recent it was.

7. Change in Maps
A powerful earthquake, like the one in Haiti, can “render current maps out of date, posing additional challenges to rescue workers on the ground. New satellite images can help rescue efforts by providing updated views of how the landscape has been affected,” as this recent article from sciencedaily.com explains.

Source: Science Daily, USGS, NEIC

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Originally Published in Reader's Digest