Quaking animals

I thought you might be interested to know how my dog reacted if thats what he was doing. Shortly before I felt the vibration, the dog woke me by jumping on me and whining which made us think he had to go out. He then jumped off the bed, moved to his bed and started scratching at it. He has never scratched like that before. At that point I felt the vibration. It only lasted a few seconds and was nothing more than a mild vibration not like the shaking you hear folks talking about on the radio. My first thought was that it was more of the construction taking place near our house. If the dog hadnt pounced me, I would have slept through it, and I didnt realize it was an earthquake until I heard it on the radio. After the vibration stopped, the dog continued to scratch at the floor and his bed for a while. My wife took him out but he didnt go hes still learning thats what hes supposed to do when we take him out. He came back upstairs, jumped up on our bed and went back to sleep until about 6:00 am when he really did have to go out. Ive seen dogs scratch at their beds before, and adjust them, but this was different. The whole thing really made me wonder how they sense stuff like that, and if what he was doing was a reaction at all (because he kept scratching for a short time after it stopped), or if he was just being a puppy. Ive had dogs all my life and have never seen one react to a tremor.