Why can the same earthquake have different ratings on the richter scale and the moment magnitude scale?

The Richter scale is accurate only for small earthquakes near seismograph stations. Large or earthquakes that happens far from seismic stations have the tendencies that it doesn’t work. The Richter Scale assigns a number rating (from 1 - 10) to an earthquake. The rating is based on how fast the ground moves at a seismic station.