What modern scale is now standard for measuring earthquake magnitude?

The modern scale now standard for measuring earthquake magnitude is the moment magnitude scale.

Developed by seismologists Thomas C. Hanks and Hiroo Kanamori in 1979, it measures an earthquake’s seismic moment: the fault area that ruptures, the amount of slip, and the rocks’ rigidity. This links the number more directly to the earthquake’s physical size and energy than older methods.

The scale is logarithmic. Increasing the magnitude by one represents about ten times greater wave amplitude and roughly 32 times more seismic energy. Unlike the original Richter, or local-magnitude, scale, moment magnitude does not saturate for very large earthquakes, so it is better for comparing great earthquakes.

The Richter scale remains familiar in everyday speech and is still useful for some smaller, nearby earthquakes. Seismic intensity is different: it describes how strongly the ground shakes at a particular location, rather than the earthquake’s total size.