I can guarantee you that they come quite suddenly and can be very violent. Example: in the 1971 Slymar earthquake I was thrown out of my bed and landed on my feet! Whilst waking up, it was one of the erriest and surreal experiences that I've ever had, especially because as I was trying to make sense of what was happening, the walls were cracking, pictures falling & dishes being thrown from the cupboards to the floor.
A friend of my brother's who had a clear view of the downtown L.A. skyline said that he could clearly see the skyscrapers swaying from side to side.
He freaked out so bad that he & his girlfriend returned to Rochester, N.Y. within a couple of weeks.
During the 1992 Monrovia quake, I was suddenly awake to see & hear the falls cracking, I was out of the building in a flash. And several of my
neighbours moved to other states because of their fright from that experience was so great. BTW: that building was only 1 block from Cal-Tech where
the seismic monitoring facilities are.
Some amazing footage is of the Okland quake that caused the upper tier of the bridge to collapse. One car was literally hanging over the edge held
only by it's rear wheels.
I suppose the feeling I got is of how fragile and powerless we humans are when faced with natural disasters.