Moment Magnitude
The modern magnitude scale (Mw) based on the physical size of the fault rupture.
Moment magnitude (Mw) is the scale seismologists use for medium and large earthquakes today. It is based on seismic moment, which combines the area of fault that slipped, how far it slipped, and the rigidity of the rock.
Because it ties directly to energy, moment magnitude does not saturate the way the older Richter scale does above magnitude 7. That makes it reliable for the great earthquakes where getting the number right matters most. When this tracker or a USGS page shows a magnitude, it is almost always moment magnitude.