Don Y formulated the question :
The idea of the *ground* moving is just fascinating to me! It's one
thing to be on a man-made structure and experience motion (Harvard
Bridge, Royal Gorge Bridge, tall buildings, etc.); yet another to be on
"solid ground" and feel it move!

It IS an interesting experience! I remember a 6.2 shaker in 1970 when
the brand new freeway overpass in Northern Los Angeles fell. We were in
bed on the second floor when it hit, and I watched our building rock
back and forth, bang! bang! and the street rolled like waves for a good
2 minutes. It was fun!