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Name:  carol flintoft
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1999
Question:
Our middle school science students would like to know how the Richter Scale originated, and how the numbers relate to the severity of an earthquake.

Replies:
The Ricther magnitude was developed by Charles Richter of the California Institute of Technology in 1935. It was one of the first measures of the size of an earthquake to use seismic instruments that record the ground motion. The Richter magnitude is measured from the maximum amplitude of recorded ground motion. Ground motion is recorded on a seismograph--the larger the earthquake, the larger is the ground motion. The ground motion becomes smaller the farther the seismograph is from the earthquake, so the distance between the seismograph and the earthquake must also be taken into account. For the same distance between the seismograph and the earthquake, each unit increase in magnitude corresponds to a factor of ten increase in ground motion. For example, a magnitude 6 earthquake will produce ten times the ground motion that a magntidue 5 earthquake will produce, but ten times less ground motion than a magnitude 7 earthquake. The amount of energy released by an earthquake varies by a factor of 30 for each unit increase in the magnitude--a magnitude 6 earthquake produces 30 times the energy of a magnitude 5 earthquake and 30 times less energy than a magnitude 7 earthquake. Incidentally, a magnitude 5 earthquake produces about as much energy as the nuclear bombs dropped on Japan during World War II.

-Grant

See e.g. Bruce Bolt's book, "Earthquakes"


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