Originally Posted by
xylophone
Yep, for example here in SoCal our part of the San Andreas fault moves ~2cm a year (IIRC) and if the tension isn't released then it builds up until it is able to overcome friction and we get something nasty. This is why SoCal is due for a big quake, we haven't had a big one for a long time, basically, if you were to compare it to a pregnancy, we're 11 months pregnant.
Force of the quake =/= what you feel on the surface. A 9.0 is stronger than a 7.0 at any depth, though depth does factor into what you feel at the surface.
Also, anything short of a 7.0 is minor in active zones like Japan and here in CA. We had a 7.0 on Easter a year or two back, you can definitely feel it, but structural damage will be minimal, if there is any at all.