This is a clarification to the original question. I said that a magnitude 9 earthquake is one hundred times as strong as a magnitude 7 earthquake. The US Geological Survey website showed me the error. It's not one hundred times as strong. Rather, the measured amplitude is one hundred times as great.
The USGS site goes on to say that a whole number increment of one in the Richter scale represents about 31 times more energy. Therefore a magnitude 9 earthquake is many hundreds of times more powerful than a magnitude seven quake. The earthquake power calculator at http://www.convertalot.com/earthquake_power__calculator.html seems to show an increase in power of nearly one thousand times.... more