There are a number of earthquake magnitude scales, including the
moment magnitude scale (the scale currently favoured by
seismologists), the Richter or local magnitude scale and the
surface wave magnitude scale.
There are a number of earthquake magnitude scales, including the
moment magnitude scale (the scale currently favoured by
seismologists), the Richter or local magnitude scale and the
surface wave magnitude scale.
The use of the Richter magnitude scale has largely been replaced by the moment magnitude scale in most countries. The United States Geological Survey (USGS), for example, uses the moment magnitude scale designated as MMS or Mw to measure all large earthquakes.
UPDATE: Official magnitude was updated to 9.1 on Nov 7, 2016.
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The moment magnitude scale is more accurate for large earthquake
than can cause damage.