One earthquake. Different experiences.

Magnitude measures an earthquake’s size at its source. Intensity describes the shaking and effects at a particular location. The same earthquake can have many intensity values across the area where it is felt.

Why does the same earthquake feel different?

Distance from the rupture, earthquake depth, local ground conditions, and the way buildings respond all affect the experience. Soft sediments can amplify some shaking. A magnitude number alone cannot tell you how strongly a particular home shook.

What happened to the Richter scale?

The original Richter scale, also called local magnitude, was developed for a particular recording setup and regional earthquakes. Other magnitude types suit other circumstances. Moment magnitude, written Mw, uses an estimate of seismic moment, which relates to the fault area, slip, and rock rigidity. It is especially useful for very large earthquakes.

An app’s “M” label may summarize different magnitude types supplied by the reporting agency. It does not necessarily mean every value was calculated on the original Richter scale.

One magnitude step is a big difference

For the standard magnitude comparison, one unit corresponds to a factor of 10 in measured wave amplitude and about 32 in estimated energy. Two units correspond to factors of 100 and about 1,000 respectively.

These ratios compare earthquake size; they are not predictions of damage or of the shaking at your location.

Try the earthquake magnitude comparison calculator →

Reading an event in Explorer

Select an earthquake to find its magnitude, depth, and time. Follow its USGS link for any available shaking information. The rings on our globe encode magnitude, not the geographic area that felt shaking.