What is the standard magnitude scale used today for comparing large earthquakes?

The moment magnitude scale is the standard scale used today for comparing large earthquakes. It was developed in the 1970s by Hiroo Kanamori and Thomas C. Hanks to provide a more physically meaningful measure than local magnitude for major events.

Moment magnitude is calculated from seismic moment, which depends on the fault’s rigidity, the area that slipped, and the average amount of slip. Because it is tied to the physics of the rupture, it remains useful for very large earthquakes that can exceed the practical range of the original Richter local-magnitude scale.

The scale is logarithmic. An increase of one magnitude represents ten times greater wave amplitude and roughly 32 times more energy released. Thus, a magnitude 8 earthquake is far more energetic than a magnitude 7 earthquake.

Magnitude and intensity are different. Magnitude describes the earthquake source, while intensity describes observed effects at a particular location. The Modified Mercalli scale measures intensity, not earthquake size.