What Earthquake Maps Should Really Look Like

How much more powerful is a magnitude 7 earthquake than a magnitude 3? Most maps give the wrong impression.

When we hear that a magnitude 8 earthquake has struck, we know that’s worse than a magnitude 4 earthquake. But how much worse?

It sounds like it should be twice as strong, but it's not. Actually, a quake of magnitude 8 releases a million times more energy than a magnitude 4 quake.  

That's because the earthquake scale—called the Moment Magnitude Scale, which replaced the Richter Scale—is logarithmic, rather than arithmetic. If you don't remember logarithms from school, each number on a logarithmic scale represents a factor of ten, so a magnitude 8 earthquake shows up on a quake-measuring seismometer as ten times larger than a magnitude 7. And it releases more than 30 times as much energy.

This isn’t an unusual way

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