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Moment Magnitude Explained—What Happened to the Richter Scale?

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Published on Sep 4, 2012

www.iris.edu/educate
Scientists have developed far-more sensitive seismometers that, with faster computers, have enabled them to record & interpret a broader spectrum of seismic signals than was possible in the 1930's, when the Richter magnitude was developed. The Richter Magnitude Scale is effective for nearby earthquakes below magnitude 7, but not for larger earthquakes. The Moment Magnitude Scale uses seismograms plus what physically occurs during an earthquake (which can also be derived from seismograms), known as the "seismic moment". The seismic moment defines how much force is needed to generate the recorded waves. That information is plugged into the moment magnitude scale to give us the amount of energy that is released during an earthquake.

For an interactive magnitude calculator, please visit: http://www.iris.edu/edu/10.5/EQSimula...

Directed by Robert Butler, University of Portland OR
Animation by Jenda Johnson, Earth Sciences Animated
Narrated by Roger Groom, Mt. Tabor Middle School, Portland OR
Original music by Jesse Gay, CNS Engineering
Photographs courtesy of US Geological Survey
Reviewed by Robert Lillie, Oregon State University and Kaz Fujita, Michigan State University

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