To follow up on what Roger is saying, remember that the magnitude scale is logarithmic. Each whole point in magnitude is about 32 times in energy released. 2 whole points is exactly 1000, so actually 1 point is the square root of 1000 (31.622776.....)

The point being, it takes 1 million 1.4 quakes to equal the same amount of energy as a mag 5.4 quake. Or, 1000 3.4 quakes to equal one 5.4. It is clear from the record that there are not that many smaller earthquakes between the larger ones. That's why enough energy can still build up to make the larger quake even though smaller ones still occur.

It doesn't matter how the fault is locking up - big rocks vs small rocks or what-have-you. Just think about the energy release. That energy is being stored somehow, it doesn't matter how. It still takes 1000 M3.4's to equal 1 M5.4.

Brian