Scientists largely use the moment magnitude scale to categorize earthquakes’ strength and size in a way that’s more accurate than the long-used Richter scale, the US Geological Survey says.

The scale has no upper limit, but no fault long enough to generate a magnitude 10 earthquake is known to exist, according to USGS. In some cases, earthquakes can be so small as to have a negative ...

So a 9.5-magnitude quake — such as the one that occurred in Chile in 1960, the strongest ever recorded — is more than 30,000 times more powerful than a 6.5-magnitude quake, which itself can be ...