Richter Scale vs Moment Magnitude
Why news still says Richter but scientists use moment magnitude, and when the difference actually matters.
Both are ways to put a single number on an earthquake's size, but they measure it differently and one has largely replaced the other.
The Richter scale
Charles Richter introduced his scale in 1935, based on the amplitude of waves recorded on a specific type of seismograph in Southern California. It worked well for moderate, local quakes. Its weakness is saturation: above about magnitude 7, the scale stops increasing meaningfully even as quakes get far larger. A magnitude 8 and a magnitude 9 can look almost the same on Richter, which is a serious problem for the events that matter most.
Moment magnitude
Moment magnitude (Mw), developed in the 1970s, fixes this. It is based on seismic moment, a physical measure combining the area of the fault that slipped, how far it slipped, and the rigidity of the rock. Because it ties directly to the energy released, it does not saturate. A magnitude 9.5 like the 1960 Chile quake gets the number it deserves.
When the difference matters
For everyday small quakes the two scales give nearly identical numbers, which is why "Richter" survives in headlines without causing harm. The difference only becomes important for great earthquakes, where Richter undercounts and moment magnitude tells the truth. When you see a magnitude on this tracker, it is moment magnitude, calculated by USGS.
The takeaway
Use "magnitude" rather than "Richter" if you want to be precise, and remember the logarithmic nature either way. The scale matters less than understanding that each whole step is about 32 times more energy.