From the FAQ:
The tides exist due to a slight see-saw effect on the earth. As it goes back and forth, the water rushes to the side that is lower. Note, this is a very slight wobble. Remember, these wobbles are created by very minor earthquakes. They keep the tides in check. Notice that large earthquakes result in large tides or "tsunami
what keeps these earth quakes regular? im almost certain earth quakes are not a "regular" occurance.