I'm doing some research on this topic, which was how I came across this page, and it seems like you seem to not understand the Richter Scale, which I will admit, is at some times confusing. The force of a magnitude 8 earthquake is Not actually only 4 times worse than that of a magnitude earthquake. In fact, it is 100000 times worse! As I quote http://www.sms-tsunami-warning.com/pages/richter-scale :
"How is the Richter Scale calculated
The Richter magnitude involves measuring the amplitude (height) of the largest recorded wave at a specific distance from the seismic source. Adjustments are included for the variation in the distance between the various seismographs and the epicentre of the earthquakes.
The Richter scale is a base-10 logarithmic scale, meaning that each order of magnitude is 10 times more intensive than the last one. In other words, a two is 10 times more intense than a one and a three is 100 times greater. In the case of the Richter scale, the increase is in wave amplitude. That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake."