Magnitude Explained: Moment Magnitude vs. Richter Scale

What happened to the Richter Scale?

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 moment magnitude 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.

Keypoints:

• Richter Scale is mostly effective for regional earthquakes no greater than M5
• Moment Magnitude is more effective for large earthquakes Moment Magnitude uses more variables to calculate the energy released using seismic moment
• Seismic moment combines the seismic energy with offset on the fault and rigidity of rock
• Noodles can be used to teach relative magnitude

Level: Novice

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Understanding the magnitude change, thus the relative energy released from say, magnitude 7 to magnitude 8 can be challenging. Dr. Robert Butler (Univ. Portland) uses spaghetti to illustrate the concept by breaking pasta to show how each step up in magnitude represents a huge jump in the size of the pasta bundles. Each step in magnitude is represented by 32 times more spaghetti noodles.

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