Forgot to mention - there's a way to tell whether you are feeling a small quake centered nearby, or a larger quake with a distant epicenter. The first shock waves (P- and S-waves) emitted from a quake travel in a straight line; they have a sort of rapid, "buzzy" feel, very sharp. After that come the Rayleigh waves, which travel more slowly around the surface of the Earth - so the more distant a quake is, the longer the time lag before you feel them. If the epicenter is nearby, you won't feel any time lag at all, and probably won't feel the difference between the two sets of waves - just one period of shaking. If you feel an early jolt followed by gradually increasing shaking, it's likely the epicenter is distant and the quake is large. (If you're too far away you won't feel those early waves at all, only the later surface waves.)

In the aforementioned Loma Prieta quake, the initial jolt felt much like a small quake on the nearby Hayward Fault; but when the rocking motion started up a few seconds later, I knew it was a big quake.