Since the 1960s, seismologists have stopped using the famous Richter scale, preferring to use a moment magnitude scale, which ...

Using that scale, the U.S.G.S. reported a maximum shake value of just over 6 — or “strong” — near the epicenter on Friday, and that people felt shaking across the region.

About 55 earthquakes a day – 20,000 a year – are recorded by the National Earthquake Information Center. A quick guide to how they are measured.

The readings are communicated in terms of magnitude, and the intensity, based on the effects on people and structures, is communicated with the Modified Mercalli (MM) Intensity Scale.