Earthquake magnitudes are measured using the Richter Magnitude Scale. On this scale (ranging from 0-10), anything below 4.9 can cause some shaking, but usually doesn't cause damage. These are minor quakes. An earthquake ranging from 5.0 - 5.9 can cause significant damage to poorly constructed buildings, and strong quakes from 6.0 - 6.9 can be destructive in a 100 mile diameter. 7.0 -7.9 magnitude earthquakes only occur about 180 times a year. These are substantially destructive. Anything above that (8.0-10.0) is highly uncommon, or has never happened.