The poor cats don't think much of it.
Wait until they start slinking around the house with their undercarriages half-retracted and their bellies dragging on the carpet. Then you'll know it was a REALLY decent earthquake. Friends in Christchurch tell me that's what their cats used to do when a really big one hit. They used to look at the cats whenever the ground shook to see whether it was a big one or not.
However, I didn't feel a thing....I'm parked at Auckland Airport waiting to board a flight to Masterton in about twenty minutes or so.