Answer:
Essentially, each successive magnitude is 33 times larger than the last. That means a magnitude-8.0 earthquake is 33 times stronger than a 7.0, and a magnitude-9.0 earthquake is 1,089 (33 x 33) times more powerful than a 7.0 — the energy ramps up fast.
The magnitude 7 earthquake is 100 times as strong as the magnitude 5 earthquake. The 100 comes from the increase in the scale from 5 to 7, which is an increase of 2, so you multiply the strength of the weaker earthquake by 107-5 = 102 = 100, and that gives you the strength of the stronger earthquake.
