The Richter and Moment Magnitude scale are both logarithmic scales so that a scale 1 earthquake would be 10 times weaker than a scale 2 earthquake and 100 times weaker than a scale 3 earthquake, so mathmatically I would say that it increases by a tenth of a scale 7 earthquake.
The earthquake in Japan lasted about 3-5 minutes.
3
Seismic energy increases by a factor of about 31.6 for each increase of magnitude, so a magnitude 3 earthquake has 31.6 times more energy released than a magnitude 2 earthquake.
3 stations
An earthquake that was rated 3 on the Richter scale would beignored
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