The last major earthquake to strike Tokyo was in September 1923, when the magnitude 7.9 Great Kanto Earthquake rattled eastern Japan for 10 minutes and led to the deaths of as many as 140,000 people.
http://www.telegraph.co.uk/news/worldne ... aster.html
This doesn't make it clear whether the 140,000 were all in Tokyo, or were spread out over 'eastern Japan'. This is about double the estimate given by Crawford Sams for the deaths by the 'atomic bomb' in Hiroshima. So maybe, Hiroshima and Nagasaki put together didn't equal one earthquake?
This says 'up to' so I don't know the range of estimates. Of course, there's also a wide range of estimates for the bombing of Hiroshima.