A couple of earthquake updates from this afternoon's (1:48pm) temblor: The magnitude has been adjusted to 3.8. Also, many people reported hearing a "thunder" sound (ring video from Stephanie Slack) just before the shaking. This was a shallow quake (depth was 6km, or 3.7 miles). Sound waves can travel faster than the motion, thus hearing it before feeling it, and since the energy was closer to the surface, with less "earth" to insulate the sound, it produced what many of us heard this afternoon.