Northridge earthquake, 1994. Magnitude 6.7. Equal to 5.6 megatons
Sichuan earthquake, 2008. Magnitude 7.9. Equal to 600 megatons
The Richter Scale is logarithmic. Thus, an 8.0 can be hugely more destructive than a 7.0.
I was in L.A. during the Northridge quake. It did tremendous damage. But this China quake was vastly more powerful than that.