The 6.9 Loma Prieta earthquake killed 63 people and left thousands homeless in California in 1989.

What made that quake significant was the duration (it went on for 15 seconds). That's a factor that supersedes the strength of the quake to an extent. Because a weaker quake will cause more damage over a long period of time.

Put it this way: Hit a wall with a hammer and you might cause a dent. Continually hit that wall with a hammer for 15 seconds and you'll probably break through.

The 2001 earthquake in Gujarat lasted for more than 2 minutes and killed around 20,000 people. The quake struck early in the morning during India's Republic day celebrations. The authorities said that the long duration caused more damage http://en.wikipedia.org/wiki/2001_Gujarat_earthquake

And the 2011 Christchurch Earthquake was 6.3 - killing 181.

It's not just about the size - it's about where it actually hits. (Note that Christchurch had a 7.1 quake six months earlier with 0 deaths)

And when: the 7.1 struck about 4:30am Saturday morning--the outcome would've been very different if it had also struck at ~12:50pm weekday as the 6.3 did.