The Bam quake, which killed 31,000 people, was rated about 6.6 on the Richter scale. The Japan quake has been re-rated this week at 9.0. But the Richter scale is logarithmic so that a 9.0 quake is 10 times more powerful than an 8.0 quake, 100 times more powerful than a 7.0, and a 1,000 times more powerful than a 6.0 quake.
