Earthquakes

Charles Richter determined that the seismic waves emitted from an earthquake could be used to estimate its magnitude, and he developed a calibrated system for measuring these waves commonly known as the Richter Scale (Earthquakes). The Richter Scale formula is based on the discovery that the larger the earthquake, the larger the amplitude of ground motion at a given distance from the quake. The Richter Scale equation is:

R (x) =.67 • log (.37x) + 1.46

R (x) equals the magnitude of that earthquake on the Richter scale and x equals the energy of an earthquake in kilowatt-hours (Earthquakes). The small numeric differences in values of R (x) can be misleading if one does not understand that the scale is logarithmic, which means that each whole number of the scale actually increases by 10. Thus, a magnitude 7.0 earthquake is ten times stronger than a 6.0; a 7.0 is 100 times greater than a 5.0; and a 7.0 is 1000 times greater than a 4.0.

In the United States, California receives the most attention for earthquakes, but Alaska actually has had eight of the largest ten earthquakes in this country. The largest was a magnitude of 9.2 at Prince William Sound Alaska on March 27, 1964 (The largest earthquakes in the United States). This earthquake triggered a Pacific-wide tsunami. The earthquake and resulting tsunami took the lives of 115 people (Earthquake facts and follies). It raised or lowered the ground surface as much fifty-six feet in some areas. The length of the ruptured fault was between 310.5 and 621 miles. To put the magnitude of this earthquake in perspective, the amount of energy released was equal to 12,000 Hiroshima-type blasts, or 240 million tons of TNT. The 9.1 magnitude was more than 10,000 times greater than a moderate 5.0 earthquake.

Bibliography

Earthquake facts and follies. Retrieved May 21, 2006 from Web site: http://www.ceri.memphis.edu/public/follies.shtml

Earthquakes. Retrieved May 21, 2006 from Web site: http://www.teachervision.fen.com/natural-disasters/earth-sciences/6125.html

The largest earthquakes in the United States. Retrieved May 21, 2006 from Web site: http://www.infoplease.com/ipa/A0193595.html