Roger,

Have you ever seen a chunk of wood floating on an ocean wave?

Present theories are that this is what is happening to Shan's and other people's houses.

The Solid Earth Tide waves are moving strain data related to approaching earthquakes probably from east to west. As the strain waves pass Shan's house it twists and turns a bit. And that causes the displacements in the path of the sun's shadow cast on his interior wall. They don't result from the entire Earth rocking back and forth.