Alaska Volcano Observatory

Here's a helpful picture for thinking about the size of earthquakes. We usually talk about the amount of energy released in an earthquake as the "earthquake magnitude (M)". But, earthquake magnitude is on a logarithmic scale. That means a M2 earthquake releases as much energy as about 32 M1 earthquakes. Likewise, about 32 M2 earthquakes release the energy of one M3 earthquake. Now consider that a M3 earthquake releases about 1000 times the energy of a M1. As you go up the magnitude scale the numbers get gigantic - one billion M1 earthquakes release the energy of a M7 earthquake! Volcanic earthquakes tend to be really small, usually less than M3. But remember, if a volcano usually has only M1 earthquakes, and then has a M2 - this volcano has released about 32 times more energy than usual. This is why AVO seismologists closely watch even the smallest earthquakes to look for changes at a volcano.

Image courtesy of the AVO/UAF-GI.
Please cite the photographer and the Alaska Volcano Observatory / University of Alaska Fairbanks, Geophysical Institute when using this image.
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